ALTERNATE-CUEREp, ; ;  /, 

MACHINERY. 


GISBERT  KAPP,  Assoo:  M.  INST.  C.  E. 


Reprinted  from  the  Minnies  of  Proceedings  of  the  Insti- 
tution of  Civil  Engineers,  London. 


NEW   YORK: 

D.    VAN    NOSTRAND    COMPANY, 
28  MURRAY  STREET  AND  87  WARREN  STREET. 

1889. 


: -.-.:: 


PREFACE. 


The  subject  comprised  under  the  title 
of  this  monograph  naturally  divides 
itself  into  the  following  sub-sections : 
1.  Alternators ;  2.  Transformers  ;  3.  Mo- 
tors ;  4.  Meters ;  5.  Mains ;  and  6. 
Accessory  apparatus  for  use  in  central 
stations  and  on  the  premises  of  the  per- 
sons supplied  with  current  from  such 
stations.  The  question  of  lamps  does 
not  properly  belong  to  the  subject  under 
consideration,  because  glow  lamps  are 
equally  suitable  to  be  fed  by  alternating 
and  direct  currents,  and  the  alterations 
required  to  make  arc  lamps  work  with 
alternating  currents  are  easily  applied, 
and  present  no  special  interest;.  In  the 
present  volume,  the  author  deals  more 
especially  with  the  first  three  subjects, 
namely,  alternators,  transformers,  and 
motors. 


x*°^ 

nriiTiftsiTin 

\4^v&$£r 

ALTERNATE-CURRENT  MACHINERY. 


BY  GISBERT  'K&PP,  Assoc.  M.  INST.   C.  E. 


ALTERNATORS. 

The  theory  of  alternate-current  ma- 
chines, as  given  in  modern  text  books,  is 
based  upon  the  assumption  that  the  cur- 
rents are  generated  in  wire  coils,  the 
magnetic  induction  through  which  under- 
goes periodical  changes  according  to  a 
simple  sine-function.  A  machine  of  this 
character  would  be  represented,  in  its 
most  elementary  form,  by  a  coil  of  in- 
sulated wire  revolving  round  an  axis  in 
its  own  plane,  with  uniform  velocity  in  a 
uniform  magnetic  field,  the  axis  of  rota- 
tion being  at  right  angles  to  the  lines  of 
the  field.  Fig.  1  represents  such  a  ma- 
chine ;  a  rectangular  coil  A  B  is  placed 
in  the  field  produced  by  the  polar  sur- 
faces N  S,  and  if  these  surfaces  extend 


6 

beyond  the  space  occupied  by  the  coil, 
the  field  within  that  space  may  be  con- 
sidered to  be  uniform.  If  the  axis  of 
rotation  passes  midway  between  the  sides 
A  and  B  of  the  rectangle,  the  electro- 
motive forces  in  both  branches  of  the 
coil  are  added,  and  the  total  electro- 
motive force  at  any  moment  is  according 
to  a  well-known  formula — 

r 

e  =  2  7t  n  z  -  sin  a (1), 

2 

where  n  is  the  frequency  (number  of 
complete  periods  per  second),  T  is  the 
number  of  wires  in  both  branches  A  and 
B  of  the  coil  collectively,  z  the  total 
induction  through  the  coil  when  the  lat- 
ter stands  at  right  angles  to  the  lines  of 
force,  and  a  the  angle  between  this  posi- 
tion and  the  position  at  which  the  elec- 
tromotive force  e  is  generated.  The  re- 
lation between  a  and  £,  the  time  which 
was  required  to  rotate  the  coil  through 
this  angle,  is  a  =  2  7t  n  t.  The  total 
electromotive  force  changes  periodically 
from  a  positive  maximum  through  zero 


to  a  negative  maximum  and  back  again, 
and  the  numerical  value  of  these  maxima 

r 
is  2  n  n  z  -  (2).     For  practical   purposes 

2 


this  value  is,  however,  of  less  importance 
than  the  mean  value  of  the  electromotive 


force ;  for  on  the  latter  depends  the 
amount  of  work  obtainable  from  the 
apparatus.  By  mean  value  of  the  elec- 
tromotive force  of  an  alternating  current 
is  meant  the  electromotive  force  of  a 
direct  constant  current,  which  vvill,  in  a 
given  resistance  free  from  self-induction 
(say  for  instance,  the  wire  of  a  Cardew 
voltmeter),  produce  the  same  amount  of 
heating.  It  is  necessary  that  the  resist- 
ance should  be  comparatively  large,  in 
order  to  limit  the  current  to  such  a 
small  value  that  the  disturbing  effect  of 
self-induction  may  be  neglected.  Let  T 
be  the  periodic  time,  then  e,  the  mean 
value  of  the  electromotive  force,  is  found 
from  the  equation — 

T 

2"  2 

f  -/2  nn  zrsin  2  n  n  t\dt  =  _  ~e\ 

when  R  denotes  the  resistance  of  the 
Cardew  voltmeter. 

The  solution  of  this  equation  is  a 
simple  mathematical  operation,  and  need, 
therefore,  not  be  given  at  length.  The 
result  is 


e  =     _  11  ZT (3) 

^2 

It  is_convenient  to  compare  this  value 
with  that  representing  the  electromotive 
force  of  a  direct- current  machine  having 
the  same  field  and  external  number  of 
wires  r  (but  equally  distributed)  on  the 
armature.  The  electromotive  force  of 
such  a  machine  is  given  by  the  product 

N 

z  r  -    -  ,  where  N,  the  number  of  revolu- 
60 

tions  per  minute,  may  obviously  be  re- 
placed by  6(M  when  the  machine  has 
two  poles,  because,  in  this  case,  fre- 
quency and  number  of  revolutions  per 
second  are  identical.  If  the  direct-cur- 
rent machine  has  more  than  one  pair  of 
poles,  say,  for  instance,  p  pairs,  then  it 
is  possible  to  wind  the  armature  in  such 
a  way  that  the  electromotive  forces  due 
to  the  different  pairs  of  poles  are  added, 
so  that  the  total  electromotive  force  is  p 
times  the  above  value,  and  the  same  may 
obviously  be  done  with  the  similar  ma- 
chine wound  for  alternating  currents  so 


10 

that  in  all  cases  the  ratio  between  the 
electromotive  forces  of  the  two  machines 

remains  the  same,  namely,    ——(4\        Of 

V2 

two  machines  containing  the  same 
amount  of  material,  the  one  which  is 
wound  to  give  alternating  currents  will 
therefore  produce  about  two  and  a  quar- 
ter times  the  electromotive  force  of  that 
wound  for  continuous  current.  Since 
the  halves  of  the  armature-conductor  in 
a  direct-current  machine  are  grouped  in 
parallel,  the  strength  of  current,  which 
such  a  machine  gives  when  the  current 
density  is  the  same  as  in  the  armature  of 
an  alternator  of  equal  dimensions,  is 
twice  that  of  the  latter,  so  that  the  out- 
put of  the  alternator  will  only  be  about 
12  per  cent,  greater  than  that  of  a  direct- 
current  dynamo  of  equal  weight.  This 
result,  it  should  be  remembered,  has 
been  obtained  on  the  basis  of  the  theory 
of  alternators  as  found  in  text-books, 
whilst  neglecting  self-inductions,  dis- 
tortions of  field,  and  other  disturbing 
elements ;  and,  before  it  can  be  accepted 


11 

for  actual  practical  work,  it  is  necessary 
to  inquire  whether  the  basis  of  this 
theory  is  in  accord  with  the  constructive 
data  to  be  found  in  modern  machines  of 
this  class.  Alternators  as  now  con- 
structed are,  with  a  single  exception, 
multipolar  machines.  This  exception  is 
the  high-speed  dynamo  of  the  Hon. 
Charles  A.  Parsons,  Assoc.  M.  Inst.  C.  E., 
which  can  be  converted  into  an  alterna- 
tor by  some  slight  changes  in  its  arma- 
ture and  commutator ;  but  all  the  other 
machines  now  in  practical  use  have  more 
than  one  pair  of  poles,  which  are  set  in  a 
circle,  and  are  so  arranged  that  the  coils 
of  the  armature  sweep  past  them.  As 
the  interpolar  space  is  always  very  small, 
the  density  of  lines,  emerging  from  or 
entering  the  polar  surfaces,  may  be  taken 
as  fairly  uniform  over  the  extent  of  these 
surfaces.  It  thus  becomes  possible  to 
determine  for  every  shape  of  coil  the 
configuration  of  polar  surface,  which  will 
produce  that  variation  in  the  induction 
corresponding  to  the  simple  sine-func- 
tion, taken  as  the  basis  of  the  text-book 


12 


theory  of  alternators.  In  the  most 
simple  and  most  frequently  occurring 
case  of  a  coil  with  straight  sides,  it  is 
obvious  that  the  dimension  of  the  pole- 
piece,  which  is  parallel  to  the  active  part 
of  the  coil,  would  have  to  vary  according 
to  a  sine-function  as  shown  in  Fig.  2, 
where  ABCD  represents  the  coil,  and  PP 
the  mean  pitch  line  through  the  poles 
straightened  out.  The  shaded  areas  N 
S  are  the  poles,  which  are  shown  on 
opposite  sides  of  the  pitch-line  to  make 
their  sinoidal  contour  at  once  apparent. 
Poles  of  this  shape  are,  however,  not 
used  in  practice ;  the  poles  are  either 
trapezoidal,  circular,  or  rectangular.  In 
the  Mordey  alternator  the  poles  have  a 
trapezoidal  face,  and  those  succeeding 
each  other  on  the  same  side  of  the 
armature  are  of  the  same  sign,  and  are 
placed  in  line  with  those  of  opposite  sign 
on  the  other  side  of  the  armature.  Thus 
along  the  mean  pitch  line,  uniform  fields 
alternate  with  spaces  in  which  there  is 
no  induction;  this  arrangement  when 
straightened  out  may  be  represented  by 


13 


a  succession  of  rectangles,  as  in  Fig.  3, 
placed  above  and  below  the  line  PP,  the 
height  of  the  rectangles  representing 
half  the  induction  between  the  poles. 
The  analogue  arrangement  of  poles  in  a 
direct-current  machine  is  shown  in  Fig.  4, 
where  a  cylindrical  armature,  provided 
with  an  iron  core,  is  completely  sur- 
rounded by  its  pole-pieces.  In  the  latter 
class  of  machines  the  exact  shape  of  the 
poles  is  only  in  so  far  of  importance  as 
it  affects  the  leakage  of  magnetism,  but 
for  a  given  total  induction  through  the 
armature  the  shape  has  no  influence  on 
the  electromotive  force.  Hence  for  a 
direct- current  machine,  apart  from  the 
question  of  leakage,  Fig.  3  is  as  good  an 
arrangement  as  Fig.  1,  but  for  an  alter- 
nator it  is  not  so  good.  A  simple  calcu- 
lation, which  need  not  be  reproduced 
here,  shows  that  the  electromotive  force 
of  the  arrangement  represented  by  Fig.  3 
is 

e=Znzr (5). 

In  this  case  the  electromotive  force  is 
therefore  only  twice  that  of  the  direct- 


14 

current  machine,  and  as,  owing  to  the 
concentration  of  armature  windings  into 
one  coil,  the  limit  of  current  as  deter- 
mined by  heating  will  be  reached  sooner, 
the  current  will  be  somewhat  smaller 
than  half  that  of  the  direct-current  ma- 
chine, so  that  the  output  will  be  slightly 
less.  It  must  also  be  borne  in  mind  that 
a  rectangular  field  with  sharp  corners 
cannot  be  obtained.  In  consequence  of 
leakage  and  spreading  of  lines,  the  cor- 
ners of  the  field  will  be  more  or  less 
rounded,  as  shown  by  dotted  lines,  and 
this  circumstance  must  lower  the  elec- 
tromotive force  beyond  its  theoretical 
value.  On  these  grounds  it  would  there- 
fore appear  that  this  configuration  of 
field-magnets  is  not  very  advantageous, 
but  there  are  certain  other  considerations 
which  tend  to  modify  this  conclusion. 
In  actual  machines  it  is  not  a  single  coil 
which  has  to  be  dealt  with,  the  active 
wires  in  which  occupy  only  a  very  nar- 
row space,  but  wide  coils  covering  a  con- 
siderable extent  of  surface  on  the  arma- 
ture ;  there  is  also  the  question  of  self- 


15 

induction  to  be  taken  into  account,  and 
the  more  or  less  economical  way  of  pro- 
ducing the  field.  It  is  especially  with 


regard  to  the  latter  consideration  that 
alternators  of  this  type  (of  which  the 
Kennedy  and  Mordey  machines  are 
examples)  have  a  considerable  advantage, 


16 

as  their  fields  can  be  made  on  the  "  iron- 
clad principle,"  so  that  no  magnetism  is 
lost  in  external  leakage,  and  only  one 
coil  of  exciting  wire  is  required. 

The  type  of  field  most  commonly  used 
in  modern  alternators  is,  however,  one 
in  which  N  and  S  poles  succeed  each 
other  around  the  armature,  and  in  its 
simplest  form  such  a  machine  is  repre- 
sented by  Fig.  5,  where  an  iron-cored 
cylindrical  armature  revolves  between 
poles  which  do  not  completely  surround 
it.  The  portion  of  the  armature  not 
embraced  by  the  poles  may  be  taken  as 
equal  to  that  embraced,  and  Fig.  6  shows 
this  disposition  in  a  multipolar  machine. 
PP  is  the  mean  pitch-line  of  the  poles 
straightened  out,  and  the  poles  are  rep- 
resented by  the  shaded  rectangles  which 
have  a  width  equal  to  half  the  pitch. 
The  mean  electromotive  force  of  this 
arrangement  is 

e  =  JL#  z  T (6), 

V* 
or  183  per  cent,   greater  than  that  of  a 


17 

direct-current  machine  containing  the 
same  amount  of  material,  whilst  the  cur- 
rent, owing  to  the  concentration  of  wires, 
and  consequent  greater  liability  to  heat, 
is  something  less  than  one-half.  The 
output  of  this  machine  will,  therefore,  be 
something  less  than  40  per  cent,  greater 
than  that  of  a  direct-current  machine 
having  an  equal  weight.  It  must  not  be 
forgotten  that  the  results  here  obtained 
refer  to  machines  in  which  the  active 
wires  on  the  armature  are  concentrated 
into  single  lines.  This  is  of  course 
impossible  in  practice,  since  the  wires 
must  be  of  appreciable  thickness,  and 
must  therefore  occupy  a  considerable 
space.  An  approximation  can  be  made 
to  the  theoretical  condition  by  employing 
an  iron-cored  armature  with  projecting 
teeth,  the  coils  being  laid  into  the  re- 
cesses. As,  however,  armatures  of  this 
type  tend  to  produce  heating  of  the  pole- 
pieces,  if  the  latter  be  solid,  the  arrange- 
ment is  not  generally  used ;  and  when 
the  armature  is  provided  with  an  iron 
core,  the  surface  of  this  is  in  most  ma- 


18 

chines  perfectly  smooth.  The  wire  coils 
on  the  armature,  whether  this  contain 
iron  or  not,  must  therefore  occupy  a  con- 
siderable space,  and  this  circumstance 
will,  generally  speaking,  cause  the  elec- 
tromotive force  obtainable  with  the  dif- 
ferent forms  of  fields  now  considered  to 
be  lower  than  the  values  given.  The 
reason  for  this  reduction  is  that,  with  a 
wide  coil  not  all  the  turns  are  equally 
and  simultaneously  influenced  by  the 
field,  and  in  certain  positions  the  action 
is  differential.  The  calculation  of  the 
effective  mean  electromotive  force  for  any 
configuration  of  field  and  armature  coils 
presents  no  special  difficulty,  being  in 
fact  only  an  extension  of  the  methods 
already  indicated,  though  for  certain 
complicated  forms  the  operation  is 
laborious.  The  author  only  proposes  to 
deal  with  some  simple  cases,  which  may 
be  regarded  as  forming  the  limiting  con- 
ditions of  practical  designs.  As  regards 
the  field  these  cases  are  : 

(1)  Eectangular  field,   width  of  poles 
equal  to  the  pitch,  as  shown  in  Fig.  4. 


19 


(2)  Rectangular  field,  width    of  poles 
equal  to  one-half  the  pitch,  as  shown  in 
Fig.  6. 

(3)  Rectangular  field,  width  of   poles 
equal  to  one-third  of  the  pitch. 

As  regards  the  armature,  either  the 
whole  available  space  may  be  covered 
with  coils,  in  which  case  the  width  of 
each  group  of  conductors  forming  a  coil, 
or  one  side  of  a  coil,  will  be  equal  to  the 
pitch,  and  the  armature  will  contain  the 
greatest  possible  amount  of  wire ;  or, 
only  portions  of  the  available  space  on 
the  armature  may  be  covered  with  the 
active  conductors,  which  plan  is  generally 
adopted  in  modern  alternators,  because 
by  it  the  differential  action  alluded  to  is 
diminished.  The  cases  selected  for  con- 
sideration are  the  following : 

(1)  Width  of  coils  equal  to  the  pitch. 

(2)  Width  of   coils    equal   to  one-half 
the  pitch. 

(3)  Width  of  coils  equal  to  one-third 
of  the  pitch. 

The  calculation  of  the  mean  electro- 
motive force,  for  any  combination  of  field 


20 

and  armature  of  the  kind  here  indicated, 
is  a  very  simple  mathematical  operation, 
and  it  is  not  necessary  to  give  it  in 
detail.  It  will  suffice  to  give  the  result 
for  those  combinations  which  most 
nearly  resemble  the  conditions  found  in 
actual  practice.  As  has  been  shown,  the 
electromotive  force  of  an  alternator  can 
be  expressed  as  the  product  of  the  elec- 
tromotive force  of  a  direct- current  ma- 
chine, having  the  same  dimensions  and 
weight,  and  a  certain  coefficient  depend- 
ing on  the  configuration  of  the  field- 
magnets  and  armature-coils.  The  wind- 
ing and  other  constructive  data  of  an 
alternator  being  known,  it  is  only  neces- 
sary to  find  this  coefficient,  in  order  to 
determine  the  electromotive  force,  by 
reference  to  the  electromotive  force 
which  would  be  produced  by  the  same 
machine  if  the  armature-coils  were  con- 
nected in  such  a  way  as  to  give  a  contin- 
uous current.  In  a  paper  by  the 
author,*  read  before  this  Institution  on 

*  Minutes  of  Proceedings  Inst.  C.  E.,  vol.  Ixxxiii. 
p.  123. 


21 

the  24th  of  November,  1885,  it  was 
shown  that  the  electromotive  force  in 
volts  of  an  ordinary  dynamo  is  given  by 
the  formula : 

e  =  z  r  N  1CT6 (7), 

where  z  represents  the  total  induction  in 
English  lines  of  force  (each  equal  to 
6,000  C.  G.  S.  lines),  r  the  total  number 
of  active  wires  counted  all  round  the 
armature,  and  N  the  speed  in  revolutions 
per  minute.  If  the  machine  is  multi- 
polar,  and  if  the  different  armature-cir- 
cuits are  arranged  in  series,  the  expres- 
sion for  e  must  be  multiplied  by  p,  the 
number  of  pairs  of  poles  in  the  field. 
Let  k  be  the  coefficient  which  expresses 
the  ratio  between  the  electromotive 
forces  of  the  alternate  and  continuous- 
current  machines,  then  the  formula  for 
the  former  is — 

e  =  kpzTNW~~G (8) 

if  the  total  induction  be  given  in  English 
lines  of  force.  If  in  C.  G.  S.  units  the 
electromotive  force  is — 

e  =  kpz  r?-  10~8. 
60 


22 

The  following  table  gives  the  value  for 
k  for  different  cases,  all  referring  to  poles 
of  rectangular  shape  and  coils  in  which 
the  active  wires  are  straight : — 

1.  Width  of  poles  equal  to  pitch,  ) 
toothed   armature   and   winding  >•  k  =  2.000 
concentrated  in  the  recesses  .     .  ) 

2.  Width  of  poles  equal  to  pitch,  \ 

smooth    armature   and    winding  v  k  =  1. 160 
spread  over  the  whole  surface  .    ) 

3.  Width  of  poles  equal  to  pitch,  ^ 

smooth   armature    and  winding  I  k  =  1.635 
covering  only  one-half  the   sur-  ( 
face J 

4.  Width  of  poles  equal  to  half  the  ) 

pitch,     smooth     armature     and  !  k  =  1.635 
winding  spread  over  the  whole  ( 
surface J 

5.  Width  of  poles  equal  to  half  the") 

pitch,      smooth     armature    and  !  k  —  2.300 
winding   covering  only  one-half  ( 
the  surface J 

6.  Width  of  poles  equal  to  one-third  ] 

the  pitch,  smooth  armature  and  \k  =  2.830 


winding  covering  only  one-third 


I- 


of  the  surface J 

According  to  the  ordinary  sine-formula 
the  coefficient  is  k  =  2.220;  and  this 
agrees  fairly  well  with  case  5,  which  is 
the  most  frequently  met  with  in  actual 
practice.  The  formula  for  e  presupposes 


23 

the  knowledge  of  the  total  induction  z, 
which  depends  upon  the  shape  and  size 
of  the  field  magnets,  their  arrangement, 
the  amount  of  iron  in  the  armature,  the 
interpolar  space,  and  the  exciting  power. 
The  time  has  long  passed  when  a  con- 
sideration of  the  relation  between  excit- 
ing power  and  total  induction  would 
have  been  of  interest.  This  subject  has 
been  fully  treated  by  Drs.  J.  and  E. 
Hopkinson  before  the  Royal  Society,* 
and  the  author  has  also  dealt  with  it  in  a 
paper  on  "  The  Predetermination  of  the 
Characteristics  of  Dynamos,"  before  the 
Society  of  Telegraph-Engineers  and  Elec- 
tricians, f  These  methods  have  subse- 
quently been  improved,  by  the  introduc- 
tion of  certain  terms  due  to  Professor 
Forbes,  by  means  of  which  the  magnetic 
leakage  can  be  more  accurately  deter- 
mined. With  the  knowledge  of  the  total 
induction  2,  and  the  coefficient  k,  it  is 
thus  possible  to  determine  the  relation 


*  "  Dynamo-Electric  Machinery,"  by  Drs.  J.   and 
E.  Hopkinson     Phil.  Trans.  Royal  Society,  1888,  p.  331. 
t  Journal,  vol   xv.  1886,  p.  518. 


24 

between  exciting-power  and  electromotive 
force  of  any  given  alternator,  provided 
the  current  flowing  through  its  armature 
is  not  so  great  as  to  produce  a  sensible 
self-inductive  effect ;  in  other  words,  the 
formula  renders  it  possible  to  determine 
the  static,  but  not  the  dynamic,  charac- 
teristic. The  effect  of  self-induction  is 
to  produce  an  electromotive  force,  the 
phase  of  which  is  at  right  angles  to  that 
of  the  current ;  and  the  electromotive 
force  available  for  doing  work  in  the  cir- 
cuit is  the  resultant  of  the  induced  elec- 
tromotive force  and  that  due  to  self- 
induction.  The  mathematical  treatment 
of  the  problem  is  of  great  difficulty,  not 
only  because,  with  the  shape  of  poles  and 
armature  coils  occurring  in  modern  alter- 
nators, the  electromotive  force  is  a  very 
complicated  function  of  the  time,  but  also 
because  the  coefficient  of  self-induction 
is  not  a  constant,  but  varies  with  the 
relative  position  of  the  coils  and  poles. 
Fortunately  the  coefficient  is  compara- 
tively small.  In  machines  containing  no 
iron  in  the  armature,  such  as  the  Mordey 


25 

and  Ferranti,  it  is  almost  negligible ;  in 
machines  containing  iron  in  the  arma- 
ture, which  is  not  encircled  by  the  coils, 
such  as  the  Westinghouse  and  Lowrie- 
Parker,  it  is  still  very  small ;  and  even  in 
machines  in  which  the  coils  are  wound 
round  the  armature-core,  as  in  Kennedy's 
machine  and  that  designed  by  the  author, 
the  coefficient,  although  appreciable,  is 
yet  not  so  large  as  to  cause 'a  sensible 
error  being  introduced  by  the  assump- 
tion that  it  is  a  constant. 

The  method  originally  devised  by  Mr. 
Joubert,  for  taking  the  self-induction  of 
an  alternator  into  account,  requires  the 
solution  of  a  differential  equation,  but 
the  problem  can  be  treated  graphically 
in  a  much  more  simple  manner.  Both 
methods  have  this  in  common,  that  it  is 
assumed  that  the  current  and  all  elec- 
tromotive forces  are  sine-functions  of  the 
time.  Strictly  speaking,  this  is  not  cor- 
rect, but  the  error  is  probably  not  very 
great,  and  it  is  in  a  certain  sense  un- 
avoidable ;  because  if  this  assumption 
were  discarded,  and  each  case  treated  on 


26 


the  basis  of  the  exact  induction-curve  as 
mapped  out  from  the  shape  of  the  poles 
and  armature- coils,  it  would  lead  to  such 
difficulties  as  to  make  the  investigation 
useless  for  practical  purposes,  for  which 
easily  understood  and  simple  methods  of 
calculation  or  construction  are  wanted. 
The  sine-function  has,  therefore,  as  far  as 
the  author  is  aware,  always  been  taken 
by  previous  investigators  as  the  basis  of 
their  calculations,  and  in  this  he  pro- 
poses to  follow7  their  example. 

Let,  in  Fig.  7,  the  length  of  the  line  O 
I  represent  the  maximum  value  of  the 
current  (crest  of  the  current  wave),  and 
let  this  line  revolve  in  the  direction  of 
the  arrow  around  O  as  the  center,  with 
an  angular  velocity  w  ==  2  n  n,  then  the 
projection  of  O  I  upon  the  vertical  gives 
the  current  at  any  moment.  Let  the 
line  O  L  represent  the  maximum  electro- 
motive force  of  self-induction  due  to  the 
current  O  I,  then  the  projection  of  O  L 
will  similarly  give  the  electromotive  force 
of  self-induction  at  any  moment,  the  two 
lines  preserving  during  rotation  their 


27 

rectangular  position.  The  effective  elec- 
tromotive force  which  produces  the  cur- 
rent O  I,  through  a  resistance  having  no 
self-induction,  may  be  represented  by  a 
length  O  E  drawn  to  the  same  scale  as 
O  L,  and  since  the  effective  electro- 
motive force  must  be  the  resultant  of  the 
induced  electromotive  force  and  the 


electromotive  force  of  self-induction,  the 
former  can  be  found  by  constructing  the 
parallelogram  OLE  Et,  the  line  O  Et- 
giving  the  induced  electromotive  force 
both  as  regards  magnitude  and  position. 
If  the  length  O  E  represents  the  elec- 
tromotive force  lost  on  account  of  the 
resistance  of  the  armature,  the  remaining 


28 

portion  R  E  represents  the  electromotive 
force  actually  available  for  doing  work 
through  the  resistance  of  the  external 
circuit ;  and  this  will  the  more  nearly 
approach  the  induced  electromotive  force 
the  smaller  the  armature  resistance,  and 
the  smaller  the  self-induction  of  the 
whole  circuit.  In  order  to  obtain  a 
maximum  of  work  in  the  external  circuit 
with  an  alternate-current  plant,  it  is, 
therefore,  advantageous  that  the  armature 
of  the  alternator  should  have  a  minimum 
of  resistance,  and  that  the  total  self- 
induction  of  the  circuit  should  be  small. 
The  commercial  value  of  a  given  type  of 
alternator  depends,  amongst  other  things, 
upon  the  amount  of  work  which  can  be 
obtained  from  a  given  weight  of  materials 
employed  in  the  construction  of  that  par- 
ticular type  of  alternator.  This  value 
will,  therefore,  be  roughly  indicated  by 
the  ratio  between  the  length  of  the  lines 
R  E  and  O  E,- ;  and  this  ratio  the  author 
proposes  to  call  "plant-efficiency.''  It 
must  be  borne  in  mind  that  the  plant- 
efficiency  is  not  an  indication  of  the  more 


29 

or  less  perfect  way  in  which  the  alterna- 
tor transforms  mechanical  into  electrical 
energy,  but  merely  an  indication  of  the 
commercial  value  of  any  given  type  for 
producing  a  maximum  amount  of  exter- 
nal work  with  a  minimum  weight  and 
cost  of  the  materials  employed.  The 
electrical  efficiency  of  the  machine  can 
also  be  found  from  the  diagram.  Accord- 
ing to  a  well-known  law,  the  internal 
energy  of  the  machine  is  equal  to  half 
the  product  of  maximum  current  and 
maximum  induced  electromotive  force 
multiplied  with  the  cosine  of  the  angle 
of  lag  <£  between  the  two. 

Internal  energy  =:  ^  E,  I  cos  $, 
when  E,  is  the  maximum  value  of  the 
induced  electromotive  force  and  I  the 
maximum  value  of  the  current.  The  ex- 
ternal energy  available  for  doing  work  is 
the  product  of  the  mean  current  and 
mean  terminal  electromotive  force,  which 
is  equal  to  half  the  product  of  their 
maximum  values. 

External    energy  =  £  E  I, 
when   E  is   the  maximum  value    of   the 


30 

terminal  electromotive  force.  The  elec- 
trical efficiency  is  therefore  given  by  the 
ratio  of  the  lines  E  E  and  O  E,  which  is 
obvious  considering  the  electromotive 
force  O  K,  absorbed  in  overcoming  the 
resistance  of  the  armature,  is  the  only 
purely  electrical  loss  occurring  in  the 
armature. 

In  alternators  used  for  parallel  distri- 
bution, the  object  aimed  at  is  generally 
to  .keep  the  terminal  pressure  constant 
for  all  currents,  and  this  can  be  attained 
by  working  with  a  constant  field  and 
suitably  varying  the  speed,  or  by  main- 
taining a  constant  speed  and  adjusting 
the  exciting  current  so  as  to  suitably 
vary  the  electromotive  force.  The  latter 
plan  must  be  adopted  if  several  machines 
are  worked  in  parallel;  and  in  this  case 
the  diagram,  Fig.  7,  may  be  used  to 
determine  the  limits  between  which  the 
exciting  current  must  be  varied,  to  keep 
the  terminal  electromotive  force  constant 
for  all  loads  from  no  current  to  the 
greatest  current  the  armature  is  intended 
to  pass.  The  mean  induced  electromo-. 


31 

tive  force  e  is  found  by  Formula  1  and 
its  maximum  value  is  obviouly —  , 

E;  =  V"2  e (9). 

The  maximum  value  of  the  electromotive 

force  of  self-induction  is  given  by — 

Es  =  2  n  n  L  I   .    .    .    ."  .    .    .     (10), 

where  L  is  the  coefficient  of  self-induc- 
tion, which  can  be  determined  by  various 
well-known  methods ;  or  by  running  the 
armature  in  a  constant  field,  and  measur- 
ing the  terminal  electromotive  force  with 
and  without  a  current  passing  through 
the  armature.  The  electromotive  force 
lost  in  resistance  is  simply  the  product 
of  the  current  I  and  the  resistance  K  of 
the  armature.  With  the  knowledge  of 
these  quantities  it  is  now  easy  to  deter- 
mine the  strength  of  field  required  for 
any  current,  since,  according  to  Formula 
1,  the  field  is  proportional  to  the  induced 
electromotive  force.  For  this  purpose 
the  diagram,  Fig.  7,  may  be  used,  or  the 
modified  form  shown  in  Fig.  8.  Here  O 
A  represents  the  terminal  electromotive 
force,  which  is  to  be  kept  constant.  A 


32 

B  represents  to  the  same  scale  the  loss 
of  electromotive  force  in  the  armature 
when  the  machine  is  giving  its  full  cur- 
rent, and  O  D  the  corresponding  electro 
motive  force  of  self -induction.  Make  B 
C  parallel  with  and  equal  to  O  D,  and 
describe  circles  over  the  diameters  O  A, 
O  B,  O  D,  and  O  C ;  then  a  straight  line 


revolving  round  O  as  a  center,  in  the 
direction  of  the  arrow,  is  cut  by  these 
various  circles  in  such  a  way  that  the 
segments  represent  the  respective  values 
of  the  different  electromotive  forces  at 
any  moment.  Thus,  at  the  time  when 
the  angular  position  a  has  been  reached, 
the  induced  electromotive  force  is  Oc,  the 
effective  electromotive  force  is  Ob  and 


33 


the  terminal  electromotive  force  is  Oa, 
all  three  being  positive,  that  is,  in  the 
direction  of  the  current,  whilst  the  elec- 
tromotive force  of  self-induction  is 
negative,  and  is  given  by  the  length  Od. 
As  the  load  decreases,  the  circle  O  D 
becomes  smaller,  until,  when  no  current 
is  allowed  to  flow,  it  has  shurnk  into  a 
point,  whilst  there  is  no  loss  due  to  re- 
sistance, and  the  points  B  and  C  coincide 
with  A.  In  this  case  the  terminal  and 
induced  electromotive  forces  are  identical, 
and  the  strength  of  the  field  is  a  mini- 
mum and  proportional  to  the  length  O  A. 
At  full  output  the  strength  of  the  field 
is  a  maximum  and  proportional  to  the 
length  O  C.  Having  thus  found  the 
limits  of  the  strength  of  field  required  in 
these  two  cases,  it  is  an  easy  matter  to 
determine,  by  the  usual  formulas  con- 
necting strength  of  field  and  exciting 
power,  the  strength  of  the  exciting  cur- 
rent for  each.  It  will  be  immediately 
apparent  from  the  diagram,  that  of  two 
machines,  the  one  having  a  high  and  the 
other  a  low  plafftPefficteaox,  the  latter 


34 

will  at  full  output  require  more  exciting 
current,  and  if  the  resistance  of  its  field 
be  the  same,  this  circumstance  will  in- 
fluence the  electrical  efficiency  unfavora- 
bly. On  the  other  hand,  a  sensible 
amount  of  self-induction,  although  it 
does  reduce  the  plant-efficiency,  is  indis- 
pensable for  the  safe  working  of  alterna- 
tors in  parallel,  and  must,  therefore,  be 
regarded  as  rather  an  advantage  than 
otherwise. 

The  problem  of  parallel  working  is  of 
the  greatest  importance  for  central 
stations,  as  only  by  such  an  arrangement 
of  machines  can  absolute  continuity  of 
the  service  and  the  greatest  economy  at 
all  times  be  ensured.  Alternate  current 
distribution  should,  if  possible,  be  carried 
on  in  the  same  simple  manner  as  direct- 
current  distribution,  that  .is  to  say,  the 
Dumber  of  machines  at  work  should  corre- 
spond as  nearly  as  may  be  to  the  output  at 
any  time  ;  the  addition  or  withdrawal  of 
machines  should  not  even  momentarily 
interrupt  the  supply  of  current  to  any 
part  of  the  system  of  distribution.  These 


35 

conditions,  it  will  easily  be  seen,  can  only 
be  fulfilled  if  the  machines  are  capable  of 
working  in  parallel,  and  it  is,  therefore, 
of  considerable  practical  importance  to 
investigate  the  conditions  under  which 
alternators  may  be  expected  to  work 
safely  in  parallel.  This  subject  is  closely 
allied  with  that  of  working  alternators  as 
motors,  and  it  is,  therefore,  convenient 
to  consider  the  two  problems  jointly. 
The  analytical  treatment  of  an  alternate- 
current  motor  is  even  more  difficult  than 
that  of  an  alternate- current  generator; 
but  by  an  extension  of  the  graphic 
method,  the  question  can  be  treated  in  a 
very  simple  and  easily  understood  man- 
ner. It  is  well  known  that  an  alternator 
will  not  start  without  mechanical  assist- 
ance, but  that,  having  been  started  at  a 
speed  approximately  corresponding  to 
the  frequency  of  the  supply  current,  it 
is  kept  in  motion  when  this  current  is 
switched  on  to  its  terminals,  and  it  may 
under  certain  conditions  even  give  off 
mechanical  energy.  The  problem  in- 
volved may  therefore  be  stated  somewhat 


36 

in  this  fashion:  Given  an  alternator,  with 
excited  field  and  running  at  a  proper 
speed,  and  a  pair  of  terminals  from  which 
any  desired  strength  of  current  can  be 
obtained  at  a  constant  pressure,  and  hav- 
ing a  frequency  approximately  corre- 
sponding to  the  speed  of  the  alternator, 
what  will  be  the  condition  under  which 
the  alternator  will  fall  into  step  with  the 
supply-current,  and  what  will  be  the 
relation  between  the  current  passing 
and  the  mechanical  energy  given  off? 
Also,  how  will  this  relation  be  affected  by 
variations  in  the  strength  of  the  field  ? 
Let,  in  Fig.  9,  the  circle  Ef  represent  the 
terminal  electromotive  force,  and  the  cir- 
cle E  the  electromotive  force  induced  in 
the  armature ;  and  assume  a  certain 
current  under  which  the  electromotive 
force  of  self-induction  is  O  L  and  that 
lost  in  resistance  O  R.  Since  both 
quantities  are  proportional  to  the  cur- 
rent, their  resultant  O  A  will  for  all 
currents  form  the  same  angle  with 
the  axes,  the  point  A  being  simply 
shifted  further  out  on  the  line  Oa  if  the 


37 


current  increases.  It  is  obvious  that  the 
line  O  A.  can  also  be  considered  as  the 
resultant  of  E  and  E$,  and  the  position 
of  these  two  electromotive  forces  becomes 
thus  at  once  defined.  In  order  that  the 
machine  may  give  off  mechanical  work, 
the  induced  electromotive  force  must 


evidently  be  opposed  to  the  current,  that 
is  to  say,  it  must  lie  to  the  right  of  the 
vertical,  whilst  the  terminal  electromotive 
force  must  lie  to  the  left.  Under  these 
conditions  only  one  parallelogram  of 
forces  is  possible,  namely,  that  de- 
termined by  the  points  O  B  A  C  where 


38 

O  B  =  E  and  A  B  =  Ef.  The  mechan- 
ical energy  given  off  is  proportional  to 
the  product  O  A  and  O  D,  the  latter 
quantity  being  the  horizontal  projection 
of  O  B,  and  obviously  equal  to  B  F. 
Now  consider  what  will  happen  if 
some  of  the  load  is  taken  off  the  ma- 
chine. The  immediate  result  will 
evidently  be  a  slight  acceleration  of  the 
armature,  by  virtue  of  which  the  maximum 
electromotive  force  E  is  induced  sooner 
than  previously.  In  the  diagram  this 
effect  is  represented  by  the  advance  of 
the  point  B  towards  Bt  and  a  correspond- 
ing displacement  of  C  towards  C,.  The 
length  O  A  will  also  be  slightly  altered, 
viz.,  decreased  until  B  has  come  into  line 
with  line  Oa',  and  further  on  increased 
again.  If  the  whole  of  the  load  betaken 
off,  B  will  almost  coincide  with  Bt  and 
the  angle  of  lag  &  will  be  a  maximum ; 
but  the  length  O  A,  that  is  to  say,  the 
current,  will  not  be  materially  differ- 
ent from  its  previous  value,  as  can  easily 
be  seen  from  the  diagram.  Hence  it 
follows  that,  even  when  running  light, 


39 


the  motor  will  allow  a  considerable  cur- 
rent to  pass  ;  but,  as  the  phase  of  the 
current  lags  behind  that  of  the  terminal 
electromotive  force  by  nearly  a  quarter 
period,  the  energy  supplied  is  very  small; 
in  fact,  only  sufficient  to  overcome  the 
resistance  of  the  armature-circuit  and 
mechanical  friction.  With  an  increase  of 
load  the  armature  will  be  slightly  re- 
tarded, which  will  bring  the  point  B 
further  away  from  Bx  in  the  diagram. 
Simultaneously  the  lag  <P  will  decrease, 
and  the  current  which  is  proportional  to 
the  length  O  A  will  increase,  the  increase 
being  slow  until  the  point  B2  is  reached, 
and  afterwards  more  and  more  rapid. 
Since  the  mechanical  energy  given  off  is 
proportional  to  the  product  of  current, 
and  induced  electromotive  force  multi- 
plied by  the  cosine  of  the  angle  the  latter 
forms  with  the  current,  it  may  be  repre- 
sented by  the  area  of  the  shaded  rectangle, 
and  a  series  of  such  rectangles  for 
different  positions  of  the  point  B  on  the 
circle,  which  represents  the  induced 
electromotive  force,  can  be  determined. 


40 

In  this  way  it  is  found  that  the  mechani- 
cal energy  continues  to  grow  as  B  is 
shifted  higher  up  on  its  circle,  until  a  point 
in  the  neighborhood  of  B3  is  reached, 
after  passing  which  the  energy  decreases 
again.  Any  position  of  B  between  Bj 
and  B3  is  stable,  an  increase  or  decrease 
of  load  resulting  in  an  automatic  adjust- 
ment of  the  current  and  of  the  phases  of 
the  electromotive  forces ;  but  if  the 
machine  be  overloaded  beyond  the  point 
B3,  its  condition  is  unstable,  as  an  in- 
crease of  load,  tending  to  further  retard 
the  induced  electromotive  force,  must 
necessarily  reduce  the  capacity  of  the 
machine  for  doing  work,  and  thus  bring 
it  out  of  step  with  the  current.  Here  is 
a  danger  from  which  direct-current 
machines  are  exempt.  The  power  of  a 
direct-current  machine,  when  used  as  a 
motor,  increases  indefinitely  with  the 
current,  and  an  overload,  if  it  does  not 
last  long  enough  to  burn  up  the  arma- 
ture, does  no  harm;  but  with  an  alterna- 
tor, an  overload,  if  it  lasts  only  a  few 
seconds,  may  bring  the  armature  to  a 


41 


stand-still,  and  if  the  self-induction  is 
not  sufficient,  this  may  eventually  cause 
it  to  burn  up. 

It  has  been  shown  by  Mr.  H.  Wilde* 
and  by  Dr.  J.  Hopkinson,|  that  two  similar 
alternators  can  be  coupled  in  parallel  to 
the  same  circuit;  and  Professor  Adams 
described,  in  a  paper  read  in  1884  before 
the  Society  of  Telegraph -Engineers  and 
Electricians,  J  some  experiments  in  which 
he  succeeded  in  driving  an  alternator  as 
a  motor,current  being  supplied  by  another 
alternator  of  similar  construction.  Mr. 
"Westinghouse,  in  some  central  stations 
in  America,  has  also  worked  alternators 
in  parallel.  There  is  thus  sufficient  ex- 
perimental proof  that  such  a  method  of 
working  is  possible,  and  the  only  question 
which  remains  to  be  investigated  is 
whether,  for  safe  working,  any  very 


*  Proceedings  Lit.  and  Philosophical  Society  of  Man- 
chester. Vol.  viii.  p.  62:  and  "Philosophical  Magazine," 
January,  1869.  Fourth  Ssries.  Vol.  xxxvii.  p.  54. 

t  The  Inst.  C.  E.  Lectures  on  "The  Practical  Appli- 
cations of  Electricity."  Session  1882-83.  "Some  Points 
in  Electric  Lighting."  By  Dr.  J.  Hopkinson. 

$  Journal,  vol.  xiii.  p.  515. 


42 

delicate  adjustment  of  the  two  machines 
is  necessary.  If  such  were  to  be  the  case, 
it  is  obvious  that  the  system  would  not 
be  suitable  for  use  in  central  stations, 
where  the  service  must  be  carried  on  day 
and  night,  and  perferably,  by  a  staff  not 
composed  of  skilled  electricians.  If  a 
battery  of  alternators  be  already  running 
in  parallel,  and  it  be  desired  to  add 
another  machine,  the  obvious  precaution 
which  an  ordinary  attendant  would  take 
is  to  excite  its  field,  and  to  run  the 
machine  up  to  the  proper  speed  before 
joining  it  to  the  circuit.  Some  devices 
have  been  introduced  for  indicating  the 
coincidence  of  phases  by  means  of  glow- 
lamps,  but  as  the  use  of  these  requires 
careful  attention  and  quickness  of  per- 
ception on  the  part  of  the  operator,  it 
would  be  preferable  to  so  construct  the 
machines  that  absolute  coincidence  of 
phase  should  not  be  required.  If  each 
alternator  is  driven  by  its  own  engine, 
and  if  the  latter  is  provided  with  a  good 
governor,  there  will  be  no  difficulty  in 
obtaining  very  approximately  the  right 


43 

speed,  and  the  only  adjustment  which 
must  be  left  to  the  attendant  is  that  of 
the  exciting  current.  The  question  now 
arises,  within  what  limits  an  error  in  this 
adjustment  may  be  safe.  To  this  ques- 
tion the  diagram,  Fig.  10,  gives  the 
answer. 

In  this  diagram  the  circle  Ef  repre- 
sents as  before  the  terminal  electro- 
motive force,  and  the  line  Oa  the  direc- 
tion of  the  resultant  of  the  electromotive 
force  of  self-induction,  and  that  lost  in 
overcoming  the  resistance  of  the  arma- 
ture. The  coefficient  of  self-induction 
depends  upon  the  density  of  lines  within 
the  armature  core,  being  obviously  the 
smaller,  the  more  nearly  the  core  is 
magnetized  to  saturation.  For  a  reason 
which  will  be  explained  presently,  the 
iron  in  the  armature  of  alternators  is 
never  magnetized  to  any  considerable  ex- 
tent, the  induction  seldom  exceeding 
about  7,003  C.  G.  S.  lines,  and  as  at  this 
low  figure  the  permeability  is  not  much, 
if  at  all,  affected,  it  can  be  assumed, 
without  any  great  error,  that  the  self- 


44 

induction  is  a  constant  for  all  field  in- 
tensities which  occur  in  practice.  The 
angle  which  the  line  Oa  forms  with  the 
horizontal  may  therefore  be  taken  as 
unaffected  by  the  exciting  current,  and 
the  length  O  A  as  proportional  to  the 
current  passing  through  the  armature. 

Fir.  10 


In  fact,  by  employing  a  suitable  scale 
the  armature  current  may  be  read 
directly  off  this  line  on  the  diagram. 
Suppose  then  that  O  A  represents  the 
greatest  current  which  may  be  safely 
allowed  to  flow.  The  determination  of 
this  current  will  generally  not  depend  so 


45 

much  on  the  capacity  of  the  machine 
which  is  being  switched  on,  as  on  the 
consideration  as  to  how  much  current 
may  be  temporarily  taken  from  the  other 
machines  at  work.  A  new  machine  is 
only  added,  if  the  limit  of  output  of 
these  machines  is  in  danger  of  being* 
overtaken  by  the  demand  for  current  in 
the  whole  system ;  and  since  the  avail- 
able margin  will  therefore  necessarily  be 
small,  the  machine  about  to  be  coupled 
up  must  not  be  allowed  to  act  as  a  heavy 
drain  upon  the  other  machines.  This 
limits  the  amount  of  current  at  disposal 
for  bringing  the  new  machine  into  step. 
Let  this  maximum  current  be  represented 
by  the  line  O  A.  Before  switching  on, 
the  engine  is  started  and  run  up  to  the 
proper  speed,  in  which  case  the  only 
work  done  by  the  engine  is  that  of  over- 
coming its  own  friction,  and  the  fric- 
tional  resistance  of  the  machine.  If,  at 
the  moment  of  switching  on,  the  in- 
duced electromotive  force  occupies  a 
position  to  the  left  of  the  line  Oy,  there 
will  be  a  momentary  increase  of  currentr 


46 

and  a  considerable  retarding  action  of 
the  armature,  causing  it  to  lag  so  that 
the  induced  electromotive  force  will 
immediately  be  shifted  back  to  a  position 
on  the  right  of  Oy,  and,  finally,  as  the 
engine  is  supposed  to  give  all  the  power 
required  for  running  light,  equilibrium 
will  be  attained  by  the  induced  electro- 
motive force  occupying  a  vertical  posi- 
tion, when  no  work  is  being  done  by  the 
current.  The  question  now  is,  what 
must  be  the  induced  electromotive  force 
to  limit  the  current  to  the  value  of  OA.? 
This  is  easily  found  by  describing  round 
A  as  center  with  radius  E(,  a  circle,  and 
marking  its  point  of  intersection  E'  with 
the  vertical  Ot/.  That  strength  of  field 
which  will  give  the  induced  electromotive 
force  OE'  is  the  least  which  may  safely 
be  permitted.  The  terminal  electro- 
motive force  will  then  occupy  the  posi- 
tion OE'j,  which  line  is  parallel  with  and 
equal  to  E'A.  It  should  be  observed 
that  there  is  between  the  terminal  elec- 
tromotive force  and  the  current  a  differ- 
ence of  phase,  amounting  to  nearly  a 


47 

quarter  period.  This  circumstance  tends 
greatly  to  minimize  the  disturbing  in- 
fluence of  the  machine,  which  absorbs 
current  upon  the  other  machines  supply- 
ing current  to  the  mains.  Thus  the  idle 
machine  takes  most  current  at  a  time 
when  the  mains  take  hardly  any,  and 
when  the  mains  take  maximum  current 
that  passing  through  the  machine  is 
nearly  zero.  This  automatic  process  of 
compensation  is  valuable,  as  it  allows  the 
permissible  current,  for  bringing  the  new 
machine  into  step,  to  be  fixed  consider- 
ably higher  than  would  otherwise  be  safe. 
If,  without  increasing  the  field,  more 
steam  be  given  to  the  engine,  causing  it 
to  push  the  armature  into  a  more 
advanced  phase,  the  point  E'  will  move 
to  the  left  of  the  vertical,  and  E',  will 
move  to  the  right,  whilst  the  current  will 
increase.  As  soon  as  E't  has  passed  the 
vertical  it  opposes  the  current,  and  the 
machine  ceases  to  act  as  a  motor,  but 
acts  as  a  generator  supplying  current  to 
the  mains.  It  is  thus  possible  to  run  the 
machine  as  a  generator  in  parallel  with 


48 


the  other  machines,  notwith standing  the 
fact  that  its  field  is  considerably  weaker ; 
but  it  will  readily  be  understood  that  the 
working  under  these  conditions  cannot 
be  economical,  though  it  may  be  per- 
fectly safe.  Now  suppose  that,  instead 
of  giving  more  steam  to  the  engine,  the 
strength  of  the  field  is  increased.  The 
point  E'  will  then  be  shifted  further 
down  on  the  vertical  line  Oy,  and  the 
point  A  will  be  similarly  shifted  further 
towards  O,  that  is  to  say,  the  current 
will  be  decreased.  "When  the  field  has 
been  so  far  strengthened  as  to  make  the 
induced  electromotive  force  equal  to  the 
terminal  electromotive  force,  the  point 
E'  will  occupy  the  position  E",  and  the 
terminal  electromotive  force  the  position 
OE"f,  whilst  no  current  will  be  passing. 
If  now  more  steam  is  given,  the  machine 
will  begin  to  work  as  a  generator,  and 
the  current  will  reappear  and  attain  its 
former  value,  when  the  power  given  off 
by  the  engine  corresponds  to  the  posi- 
tion E"'  of  the  induced  electromotive 
force.  The  terminal  electromotive  force 


49 

will  then  occupy  the  position  E/". 
Under  these  conditions  the  machine  will 
work  as  a  generator,  and  much  more 
advantageously  than  formerly,  though 
not  yet  with  the  best  plant  efficiency. 
To  obtain  the  best  result  the  field  must 
further  be  streDgthened,  until  the  in- 
duced electromotive  force  occupies  the 
position  E,  and  the  terminal  electromo- 
tive force  the  position  Ef,  when  the  maxi- 
mum output  is  reached,  and  the  machine 
is  in  exactly  the  same  condition  as  the 
other  machines.  The  safe  limits,  within 
which  the  strength  of  the  field  may  be 
varied,  are  given  by  the  length  of  the 
lines  OE  and  OE',  and  the  ratio  of  the 
corresponding  exciting  currents  must 
obviously  be  still  greater  than  that  be- 
tween these  two  lines.  It  is  instructive 
to  observe  what  part  armature  resistance 
and  self-induction  take  in  determining 
this  ratio.  As  regards  the  armature  re- 
sistance, the  lower  this  can  be  made  the 
better ;  in  modern  machines  the  resist- 
ance is  generally  so  small  that  the  loss  of 
pressure  is  limited  to  from  2  to  5  per 


50 

cent,  of  the  terminal  electromotive  force. 
The  length  of  the  line  OK  in  the  diagram 
will  therefore  be,  at  most,  one -twentieth 
part  of  OE.  When  the  self-induction  is 
negligible,  the  point  A  will  almost  con- 
cide  with  O,  and  E'  will  almost  coincide 
with  E",  which  shows  that  the  safe  mar- 
gin between  minimum  and  maximum 
field-strength,  and,  consequently,  also 
between  the  smallest  and  largest  per- 
missible exciting  current,  is  extremely 
narrow.  Machines  of  this  type  can  only 
be  run  in  parallel  if  the  strength  of  their 
fields  is  adjusted  with  almost  mathe- 
matical precision,  and  as  this  would 
require  more  skill  and  attention  than  is 
available  with  the  ordinary  staff  of  a  cen- 
tral station,  such  machines  are  practically 
unfit  for  parallel  working.  To  make 
them  fit  for  this  method  of  working 
either  the  armature  resistance  or  the  self- 
induction  must  be  increased.  An  in- 
crease of  resistance,  in  order  to  be 
effective,  would  have  to  be  so  consider- 
able (as  is  easily  seen  from  the  diagram), 
as  to  seriously  prejudice  the  electrical 


51 

efficiency  of  the  machine,  and  this  expe- 
dient may,  therefore,  be  dismissed  as 
impracticable.  The  other  plan  of  in- 
creasing the  self-induction  is  not  open  to 
the  same  objection.  It  has  the  effect  of 
lowering  the  plant  efficiency,  but  its 
influence  upon  the  electrical  efficiency  is 
only  indirect,  and  so  small  that  it  may  be 
neglected.  From  the  foregoing,  it  will 
be  readily  seen  that  the  only  and  suffi- 
cient condition,  for  successful  parallel 
working,  is  a  sensible  amount  of  self- 
induction  in  the  armature  circuit.  If  the 
armature  itself  does  not  possess  this 
quality  in  a  sufficient  degree,  a  choking 
coil  of  suitable  self-induction  must  be 
inserted  into  the  circuit  of  each  machine. 
The  results  here  arrived  at,  by  a  mere 
theoretical  investigation,  are  entirely 
borne  out  in  practice.  It  is  well  known 
that  alternators  having  no  iron  in  their 
armatures  cannot  be  run  in  parallel, 
except  by  the  adoption  of  some  such 
expedient  as  choking  coils ;  also  that 
parallel  running  is  feasible  with  those 
alternators  which  have  iron- cored  arma- 


52 

tures,  and  then  with  different  degrees  of 
security.  To  make  this  point  clear, 
compare  two  machines  of  different  types 
such,  for  instance,  as  the  Westinghouse 
or  the  Lowrie-Parker  on  the  one  hand, 
and  the  Kennedy  or  the  author's  machine 
on  the  other  hand.  In  the  two  first- 
named  machines  the  coils  are  simply  laid 
on  to  the  surface  of  the  armature-core 
on  one  side,  whilst  in  the  other  two 
machines  they  completely  surround  the 
<?ore.  The  coefficient  of  self-induction 
may,  in  the  latter  case,  be  roughly  taken 
as  four  times  that  of  the  former  case, 
other  conditions  being  approximately  the 
same ;  and  it  may  therefore  be  expected 
that  parallel  working  will  be  safer  and 
more  certain  when  the  armature  con- 
ductor surrounds  the  core,  than  when  it 
lies  only  on  one  side  of  the  core,  though 
in  this  case  it  will  still  be  possible.  The 
experience  gained  in  America  with  West- 
inghouse machines  is  in  this  respect  very 
instructive.  It  has  been  found  that  the 
experiment  of  parallel  coupling  always 
succeeds  when  the  machines  are  loaded 


53 


to  about  half  their  maximum  output  or 
over,  but  that  machines  working  under  a 
less  load  cannot,  with  certainty,  be  so 
coupled.  A  glance  at  the  diagram,  Fig. 
10,  shows  the  reason  for  this.  The 
margin  of  field  strength  is  represented 
by  the  difference  in  the  length  of  the 
lines  OE'  and  OE.  This  difference  de- 
pends, to  a  great  extent,  upon  the  length 
of  the  line  OA,  which  is  proportional  to 
the  current.  If  the  current  through  the 
machines  already  at  work  is  small,  it  will 
be  further  reduced  as  soon  as  the  new 
machine  is  switched  on,  and  under  these 
conditions  the  margin  of  field  strength 
may  become  so  small,  that  a  slight 
reduction  of  the  exciting  current  of  one 
machine  may  cause  this  to  be  over- 
powered by  the  other  machines,  and 
hence  the  experiment  may  fail.  If,  how- 
ever, the  current  through  all  the  machines 
is  sufficiently  great,  then  the  margin  will 
also  be  sufficient  to  cover  such  irregu- 
larities in  the  exciting  currents,  and  in 
the  torque  of  the  engines,  as  may  be 
•expected  to  exist  when  the  plant  at  a 


54 

station  is  in  the  charge  of  ordinary 
attendants,  who  are  not  skilled  electri- 
cians or  engineers,  and  hence  the  experi- 
ment will  succeed. 

It  has  now  been  shown  how,  by  the 
aid  of  certain  diagrams,  the  behavior  of 
any  type  of  alternator,  as  regards  its 
ability  to  run  in  parallel,  can  be  ascer- 
tained ;  but,  as  the  use  of  these  diagrams 
involves  a  certain  amount  of  study,  it 
would  be  desirable  if  they  could  be 
superseded — at  least  for  ordinary  prac- 
tical work,  where  an  approximate  solu- 
tion of  such  problems  is  quite  sufficient 
— by  some  more  simple  method.  Such 
a  method  is  afforded  by  the  use  of  the 
characteristics  of  alternators.  If  a  ma- 
chine of  that  class  be  run  at  constant 
speed  on  open  circuit,  and  with  different 
strengths  of  exciting  current,  different 
terminal  electromotive  forces  are  ob- 
tained. A  characteristic  can  then  be 
plotted,  the  abscissas  of  which  represent 
exciting  power,  whilst  the  ordinates 
represent  terminal  electromotive  force, 
which  in  this  case  is  the  same  as  the 


55 

induced  electromotive  force.  Having' 
obtained  this  curve,  which  the  author 
suggests  should  be  called  the  static 
characteristic,  the  dynamic  characteristic 
of  the  machine  is  determined  for  a  cer- 
tain current  through  the  armature,  by  so 
adjusting  the  resistance  in  the  external 
circuit,  that  for  all  exciting  powers  the 
current  remains  the  same.  It  is  import- 
ant that  the  external  circuit  should  not 
contain  any  appreciable  amount  of  self- 
induction — a  condition  easily  fulfilled  if, 
during  the  experiment,  the  machine  be 
set  to  work  a  bank  of  transformers  which 
are  feeding  glow-lamps.  The  curve  so 
obtained  must  obviously  lie  wholly  under 
the  first  curve,  and  the  difference  be- 
tween the  ordinates  of  the  two  curves 
depends  upon  the  choice  of  current  for 
which  the  second  test  has  been  made, 
and  upon  armature  resistance  and  self- 
induction.  Besides  these  two  curves 
there  is  a  third,,  namely,  that  obtained 
when  the  machine  is  driven  as  a  motor 
running  light.  To  find  this  curve  it 
would  be  necessary  to  have  at  disposal 


56 

at  least  two  similar  machines,  using  the 
one  as  generator  and  the  other  as  motor, 
and  during  the  test  the  field  strength  of 
both  machines  would  have  to  be  regu- 
lated, so  as  to  keep  the  current  at  its 
predetermined  value.  Thus,  a  "  motor 
characteristic  "  would  be  obtained,  lying 
wholly  above  the  %t  static  characteristic." 
As  the  last  experiment  is,  however,  only 
possible  if  two  machines  can  be  tested  at 
the  same  time,  and  is  also  somewhat 
delicate,  another  method  of  investigation 
is  desirable.  This  can  be  done  by  using 
diagram  Fig.  10,  to  deduct  the  motor 
characteristic  from  the  two  other  curves, 
the  experimental  determination  of  which 
presents  no  difficulties  whatever,  and 
would,  indeed,  be  made  as  a  matter  of 
course  in  the  ordinary  test  of  the  ma- 
chine before  it  is  sent  out  from  the 
manufacturer.  The  static  characteristic 
gives  the  strength  of  field  for  every  ex- 
citing power.  From  the  measured  re- 
sistance of  the  armature  it  can  easily  be 
found  how  much  of  the  effective  electro- 
motive force  has  been  absorbed  in  over- 


57 

coming  this  resistance,  whilst  the  dynamic 
characteristic  shows  the  terminal  electro- 
motive force.  Thus  all  the  necessary 
elements  exist  for  determining,  by  the 
aid  of  a  diagram  similar  to  Fig.  10,  the 
length  of  the  line  O  A  and  its  angular 
position.  Having  found  the  point  A,  the 
position  of  the  point  E'  is  determined, 
that  is  to  say,  the  strength  of  field  O  E', 
which  in  a  motor  will  allow  the  prede- 
termined current  to  pass.  The  corre- 
sponding exciting  power  is  found  from 
the  static  characteristic,  and  this  gives 
one  point  of  the  motor  characteristic. 
In  the  same  manner  other  points  corre- 
sponding to  different  terminal  electro- 
motive forces  can  be  ascertained.  The 
construction  is  a  mere  geometrical  opera- 
tion, and  need,  therefore,  not  be 
explained  in  detail.  Fig.  11  shows  the 
relative  position  of  these  curves  for  one 
of  the  author's  machines,  constructed  for 
an  output  of  60  kilowatts.  For  the 
figures  from  which  the  diagram  has  been 
constructed  the  author  is  indebted  to  Mr. 
C.  E.  L.  Brown,  who  has  kindly  con- 


58 

sented  to  carry  out  an  in  dependent  series 
of  experiments,  at  the  works  of  the 
Maschinenfabrik  Oerlikon,  in  Switzer- 
land, the  electrical  department  of  which 
is  under  his  charge.  The  experiments 
were  made  as  follows :  The  alternator 
was  driven  at  its  normal  speed  of  600 
revolutions  per  minute  by  a  steam  engine, 
and  its  terminals  were  connected  with  a 

Fig.  II 


transformer  wound  to  reduce  the  press- 
ure in  the  ratio  of  20  to  1.  The  press- 
ure on  the  secondary  terminals  of  the 
transformer  was  measured  by  one  of  Sir 
William  Thomson's  balances,  specially 
made  for  alternate-current  work.  The 


59 

alternator  was  connected  with  a  bank  of 
transformers,  and  the  secondaries  of  the 
latter  with  lamps  and  other  resistances. 
A  Siemens  dynamometer  was  inserted 
into  the  armature  circuit,  and  the  second, 
ary  currents  from  the  transformers  were 
occasionally  measured  by  a  Sir  William 
Thomson's  ampere  balance.  The  primary 
and  secondary  currents  were  found  to  be 
very  nearly  in  the  ratio  of  1  to  20.  The 
exciting  current  was  adjusted  by  a  rheo- 
stat, and  measured  by  a  spring -solenoid 
instrument.  The  first  run  was  made  with- 
out external  current  in  the  armature  cir- 
cuit, except  the  small  amount  necessary  to 
record  the  pressure  by  the  stepdown 
transformer.  In  this  manner,  data  were 
obtained  for  plotting  the  static  charac- 
teristic OS.  In  the  diagram  the  excit- 
ing power  is  plotted  on  the  horizontal 
and  the  pressure  on  the  vertical.  The 
exciting  power  was  found  by  multiplying 
the  exciting  current  by  280,  there  being 
one  hundred  and  forty  turns  of  wire  on 
each  magnet-coil.  The  resistance  of  the 
armature  when  warm  is  1.74,  and  that  of 


60 

the  field  1.73  ohm.  The  bank  of  trans- 
formers, with  its  load  of  resistances,  was- 
next  switched  on,  and  the  latter  so  reg- 
ulated as  to  give  an  armature  current  of 
10  amperes  at  different  degrees  of  excita- 
tion. The  dynamic  characteristic  marked 
"  10  amperes  "  in  the  diagram  was  thus 
found.  Similar  experiments  were  made 
to  obtain  the  characteristics  at  20  and  30 
amperes,  which  are  also  shown.  Either 
of  the  three  dynamic  characteristics  can 
now  be  used  to  determine,  by  the  aid  of 
diagram  Fig.  7,  the  coefficient  of  self- 
induction  of  the  armature ;  and,  if  it 
were  not  for  certain  disturbing  causesr 
the  three  coefficients  thus  obtained 
should  be  identical.  In  reality,  this  is, 
however,  not  the  case,  chiefly  because 
the  impressed  electromotive  force  is  not 
a  true  sine  function  of  the  time.  There 
is  also  another  disturbing  element,, 
namely,  the  demagnetizing  influence  of 
the  armature  current  upon  the  field. 
When  the  machine  is  working  as  a  gene- 
rator, the  poles  developed  in  the  arma- 
ture by  the  current  itself  are  of  the  same 


61 

sign  as  the  field-poles  which  they  ap- 
proach, and  the  armature  has  therefore  a 
tendency  to  push  back  some  of  the  lines 
emanating  from  the  field-poles.  To  over- 
come this  tendency  the  exciting  current 
must  be  increased,  the  effect  being 
similar  to,  though  not  identical  with,  that 
produced  by  self-induction.  When  the 
machine  is  working  as  a  motor,  the  effect 
of  the  armature  current  is  generally,  but 
not  always,  to  strengthen  the  field-poles. 
The  author  has  selected  the  dynamic 
characteristic  at  30  amperes,  for  the  de- 
termination of  the  coefficient  of  self- 
induction  ;  because  the  great  distance 
between  this  curve  and  the  static  charac- 
teristic made  it  probable  that  the  result 
would  be  more  accurate  than  with  one  of 
the  nearer  curves.  The  coefficient  of 
self-induction  was  found  to  be  L  =  0.955 
in  C.  G.  S.  measure,  and  0.0955  in  prac- 
tical units.  Taking  this  as  a  basis,  it  is 
now  an  easy  matter  to  find,  by  means  of 
the  graphic  construction  shown  in  Fig. 
10,  the  motor  characteristic  for  any  given 
current.  A  current  of  10  amperes  was 


62 

chosen,  as  sufficiently  small  to  avoid  a 
sensible  disturbance  of  the  working  ma- 
chines when  a  new  machine  is  switched 
on,  and  this  gives  the  dotted  curve, 
marked  a —  10  amperes,"  in  Fig.  11.  The 
interpretation  of  this  diagram  is  obvious. 
The  normal  terminal  pressure  of  this 
machine  is  2,000  volts,  and  by  drawing 
the  corresponding  horizontal  line,  its 
points  of  intersection  with  the  curves 
m  s  g  fix  the  exciting  power  in  each 
case.  In  order  that  the  machine  may 
work  as  a  generator,  giving  its  maximum 
current  of  30  amperes,  the  exciting  power 
must  be  O  G.  If  the  machine  is  merely 
to  run  without  producing  or  absorbing 
current,  it  must  be  excited  to  an  amount 
represented  by  O  S,  and  if  running  idle 
as  a  motor,  and  allowing  not  more  than 
a  10  ampere  current  to  pass,  the  excita- 
tion must  be  O  M.  The  ratio  between 
the  length  of  the  lines  O  M  and  O  G 
gives,  therefore,  in  a  rough-and-ready 
way,  an  indication  of  the  degree  of  safety 
when  working  in  parallel. 

The  formulas  and  diagrams  given  above 


63 

will  be  found  sufficient  for  the  purpose  of 
designing  alternators,  or  for  the  deter- 
mination of  the  behavior  of  any  given 
machine  of  this  class,  except  in  one  par- 
ticular, viz.,  its  greater  or  lesser  liability 
to  heating.  In  any  dynamo  machine 
there  are  two  causes  for  beating,  in 
addition  to  purely  mechanical  friction. 
These  are  the  resistance  of  the  conduct- 
ors, and  the  change  of  magnetization  of 
the  iron  parts  of  the  machine.  As  re- 
gards the  first  cause,  the  result  of  which 
may  be  comprised  under  the  term  "cop- 
per heat,"  it  is  so  well  understood  that 
it  need  not  in  this  place  be  specially  con- 
sidered. One  circumstance  in  connec- 
tion with  this  subject  should,  however, 
be  mentioned.  The  liability  to  the  gen- 
erations of  eddy  currents  in  the  armature 
conductor  is  much  greater  with  alter- 
nators than  with  continuous-current  dyna- 
mos, and  in  alternators  it  varies  with 
the  construction  of  the  armature  to  a 
greater  degree.  When  the  armature 
contains  no  iron,  the  heating  from 
eddy  currents  is  much  greater  than 


64 

when  such  a  core  is  used,  and  the  arm- 
ature conductor  must  therefore  be  made 
in  the  form  of  a  very  narrow  strip  ; 
so  narrow,  in  some  cases,  that  two  or 
more  conductors  must  be  placed  in  par- 
allel to  obtain  the  required  cross-section- 
al area.  The  author  is  unable  to  suggest 
an  entirely  satisfactory  explanation  for 
the  effect  of  the  iron  core  in  reducing 
eddy  currents  in  the  copper,  and  merely 
mentions  the  fact  as  deserving  attention, 
In  direct  current  machines  he  has  ob- 
served a  somewhat  similar  phenomenon. 
When  the  pole-pieces  are  provided  with 
extensions,  the  heating  of  the  armature 
bars  is  much  less  than  when  these  exten- 
sions are  absent,  and  consequently  the 
trouble  of  heating  can  to  a  certain  de- 
gree be  overcome  by  the  simple  expe- 
dient of  fitting  so-called  u  horns  "  to  the 
pole-pieces.  Another  cause  of  the  gen- 
eration of  heat,  in  machines  of  all  types, 
is  the  change  of  magnetization  in  the 
iron  parts.  This  can  be  minimized  by 
lamination,  but  never  entirely  avoided. 
In  direct-current  machines  the  heating 


65 

from  this  cause  is,  however,  generally  so 
small  that  no  account  is  taken  of  it,  ex- 
cept when  the  induction  in  the  armature 
core  is  pushed  beyond  18,000  or  20,000. 
In  alternators  a  much  lower  induction 
already  produces  sensible  heating,  and  it 
is  for  this  reason  that  the  maximum  in- 
duction must  be  fixed  at  a  very  low  figure. 
With  a  perfectly  laminated  core,  the 
heating  is  attributed  to  an  effect  which 
Professor  J.  A.  Ewing  calls  4'  hysteresis,'' 
and  which  may  be  described  as  molecular 
friction.  This  scientist  has  experiment- 
ally determined  the  energy  required  to 
carry  certain  samples  of  iron  through  a 
complete  cycle  of  magnetization  of  vary- 
ing degree,  and  the  results  have  been  pub- 
lished in  the  Philosophical  Transactions 
of  the  Royal  Society.*  They  are  given 
in  ergs  per  cubic  centimeter ;  but  as 
these  units  are  rather  inconvenient  for 
application  in  the  workshop  or  drawing 
office,  the  author  has,  in  the  following 
table,  which  refers  to  annealed  wrought- 
iron,  translated  them  into  watts  per  ton. 

*  Phil.   Trans.  Royal  Society,  1885,  p.  523. 


66 


Induction. 

Watts  per  ton 
n  =  100. 

HP.  wasted 
in  Heat. 

2,000 

650 

0.87 

3,000 

1,100 

1.48 

4,000 

1.650 

2.21 

5,000 

2,250 

3.02 

6,000 

2,900 

3.89 

7,000 

3,750 

5.03 

8.000 

4,450 

597 

9,000 

5,550 

7.43 

10,000 

6,650 

8.90 

A  third  column  has  been  added,  show- 
ing the  HP.  transformed  into  heat,  and 
therefore  wasted  per  ton  of  armature- 
core,  if  the  frequency  is  100  complete 
periods  per  second. 

In  the  paper  referred  to  above,  Pro- 
fessor Ewing  says  that  mechanical  vibra- 
tions tend  to  decrease  the  amount  of 
energy  dissipated  per  cycle  ;  and  that,  as 
the  armatures  of  dynamo  machines  are, 
whilst  working,  in  a  continual  state  of 
vibration,  it  will  be  very  much  less  than 
indicated  by  the  figures  he  found  when 
experimenting  on  pieces  of  iron  which 
were  at  rest.  The  author,  however, 
doubts  whether  this  view  can  safely  be 
accepted.  The  vibrations  of  an  armature 


67 


are  not  of  the  sharp  character  compara- 
ble to  a  series  of  blows,  which  would 
tend  to  shake  the  magnetism  out  of  the 
core,  and  practical  experience  shows  that 
with  high  inductions  there  is  a  very  con- 
siderable amount  of  heating.  In  an  ex- 
perimental machine  which  the  author 
constructed,  the  induction  through  the 
armature  core  was  about  16,000,  and  with 
a  frequency  of  80  this  core  became 
heated  far  beyond  the  point  which  might 
be  considered  safe  in  practical  work.  In 
subsequent  machines  the  induction  was 
therefore  reduced  by  degrees,  until  a  safe 
limit  was  reached  at  about  7,000  lines 
per  square  centimeter. 

Professor  Ewing  found  that  the  energy 
dissipated  by  hysteresis  increased  with 
the  speed  at  which  the  cyclic  change  of 
induction  was  performed.  This  circum- 
stance has  not  been  taken  into  account 
in  the  preparation  of  the  table,  as  no 
exact  data  are  at  present  available,  by 
which  the  increase  of  heat  due  to  what 
Professor  Ewing  calls  "viscous  hys 
teresis"  can  be  determined.  There  is, 


68 

however,  good  reason  to  believe  that  the 
speed,  at  which  the  cyclic  change  of 
magnetism  is  performed,  has  a  consider- 
able influence  on  the  amount  of  energy- 
dissipated  in  heat  per  cycle.  It  is  prob- 
ably due  to  the  disadvantage  of  too  great 
a  speed  that  most  makers  of  alternators 
find  it  advisable  to  work  at  a  moderate 
frequency.  Another  reason  telling 
against  high  frequency  is  that  either  the 
speed  of  the  machine,  or  the  number 
of  field-poles,  or  both,  must  be  incon- 
veniently great.  A  very  high  speed  is 
mechanically  objectionable,  and  the  adop- 
tion of  a  large  number  of  field-poles 
has  the  disadvantage  of  reducing  the 
pitch,  and  therefore  of  increasing  the 
magnetic  leakage,  whilst  at  the  same 
time  lowering  the  coefficient  k,  all  of 
which  tend  to  an  increase  in  the  weight, 
bulk,  and  cost  of  the  machine.  On  the 
other  hand,  too  low  a  frequency  would 
also  tend  to  increase  the  cost  of  the 
machine,  and  there  must  therefore  be,  for 
each  type  of  alternator,  a  particular 
frequency  at  which  the  best  results  are 


obtained.  Existing  knowledge  of  the 
subject  is  not  sufficient  for  the  determi- 
nation of  this  frequency  by  a  mere 
theoretical  investigation,  but  the  experi- 
ence obtained  by  several  makers  of  these 
machines,  during  the  last  few  years,  tends 
to  show  that  the  best  frequency  for 
nearly  all  types  is  below  100.  Something 
more  will  be  said  on  this  point  later  on. 

TRANSFORMERS. 

The  theory  of  transformers  is  so  sim- 
ple, and  so  generally  understood,  that  it 
would  be  waste  of  time  to  enter  into  it  at 
length  in  this  place.  Modern  transform- 
ers are  provided  with  a  core  of  laminated 
iron,  which  is  symmetrically  placed  in 
respect  to  the  two  windings,  so  that  the 
same  induction  passes  through  both  the 
primary  and  the  secondary  coils.  Under 
these  conditions,  the  electromotive  force 
induced  in  the  two  circuits  is  simply  pro- 
portional to  the  number  of  convolutions 
they  respectively  contain,  and  the  ter- 
minal electromotive  forces  are  found 
by  adding  in  the  case  of  the  primary, 


70 

and  subtracting  *  in  the  case  of  the 
secondary,  the  loss  of  pressure  due  to 
the  resistance  of  the  coils.  In  a  properly 
designed  transformer,  this  loss  of  pressure 
should  not  exceed  about  1  per  cent,  of 
the  terminal  pressure,  so  that  the  maxi- 
mum difference  in  the  pressure  main- 
tained in  the  secondary  circuit  between 
the  lamps,  when  the  apparatus  is  used 
for  parallel  distribution,  does  not  exceed 
2  per  cent,  between  full  load  and  no  load, 
provided  the  pressure  in  the  primary 
circuit  is  kept  constant.  Such  a  small 
variation  in  the  pressure  is  well  within 
the  limits  attainable  in  direct  lighting, 
when  a  compound-  wound  dynamo  is  driven 
from  an  engine  with  a  fairly  good  gov- 
ernor, and  the  corresponding  variation  in 
the  illuminating  power  of  the  lamps  is 
sufficiently  small  to  be  tolerated.  A 
greater  variation,  especially  if  it  occur 
suddenly,  would,  however,  not  be  per- 
missible ;  and  the  question,  therefore, 
arises  as  to  what  rules  should  be  followed 
in  designing  transformers  so  that  they 
may  as  nearly  as  possible  be  self-regulat- 


71 

ing.  The  obvious  answer  is:  make  the 
resistance  of  the  circuits  as  small  as 
possible,  and  this  may  be  accomplished 
in  three  ways  :  1.  By  using  wire  of 
large  area.  This  expedient  naturally 
increases  the  weight,  bulk,  and  cost  of 
the  transformer,  and  must,  on  account  of 
commercial  reasons,  not  be  pushed  too  far. 
2.  By  employing  a  core  approximating  to 
a  circular  or  quadratic  section,  so  as  to 
decrease  the  perimeter  of  the  coils-  3. 
By  working  with  a  high  induction  or 
with  a  high  frequency. 

The  mean  electromotive  force  in  volts, 
induced  in  the  coil  of  a  transformer,  can 
be  expressed  by  the  following  formula  — 

e  =  (q)  2  n  n  z  r  lO'8  .....  (11), 

in  which  (q)  is  a  coefficient  denoting  the 
ratio  between  the  maximum  and  the 
mean  electromotive  force  (when  the  cur- 
rent-wave may  be  taken  to  follow  a  sine- 

function,    this    coefficient  is  —  _..  V  n  is 


—  _..  V 
'-t/ 


the   frequency,  z  the  total   induction  in 
absolute  units,  and  r  the  number  of  turns 


72 

contained  in  the  coil.  The  larger  3,  and 
the  smaller  n,  may  be  the  length  of  wire, 
and  therefore  its  resistance.  On  purely 
theoretical  grounds  it  would  thus  seem 
that  a  small  core  strongly  magnetized, 
and  as  high  a  frequency  as  the  alternator 
can  be  constructed  to  give,  would  pro- 
duce the  best  results.  In  practice,  how- 
ever, this  conclusion  is  wrong,  and  the 
heating  of  the  iron  core  in  consequence 
of  hysteresis  must  be  taken  into  consider- 
ation. Since  a  transformer  is  an 
apparatus  at  rest,  and  is  frequently 
placed  in  a  position  where  the  cooling 
effect  of  the  air  is  small,  the  ratio 
between  heat  generated  and  available 
cooling  surface  must  be  very  different 
from  that  permissible  in  a  dynamo,  and 
it  is  this  ratio  which  is  the  true  limit  to 
the  output  of  a  transformer.  The  arma- 
ture of  a  dynamo  is  not  subjected  to 
excessive  heating  if  a  cooling  surface  of 
about  1  square  inch  per  watt  be  provided. 
In  a  transformer,  the  amount  of  cooling 
surface  should  be  at  least  three  times, 
and  if  possible,  four  or  five  times  as  great, 


73 

especially  as  it  is  somewhat  difficult  to 
determine,  in  a  body  of  such  complicated 
shape,  what  is  and  what  is  not  effective 
cooling  surface.  From  the  table,  giving 
the  loss  by  hysteresis,  it  is  easy  to  calcu- 
late for  any  induction,  frequency,  and 
weight  of  the  active  iron  in  a  transformer, 
what  the  iron  heat  will  be ;  and,  adding  to 
this  the  copper  heat,  the  total  cooling 
surface  required  to  keep  the  apparatus  at 
a  safe  temperature  can  at  least  approxi- 
mately be  determined,  or  the  limit  of 
output  for  any  given  transformer  can  be 
approximately  found.  In  this  connection, 
it  is  instructive  to  compare  two  similar 
transformers,  one  twice  the  linear  dimen- 
sions of  the  other.  For  the  purpose  of 
the  comparison,  it  may  be  assumed  that 
in  the  small  transformer  the  iron  heat  is 
the  same  as  the  copper  heat,  though  it  is 
generally  greater.  If  the  large  transformer 
be  worked  at  the  same  induction  per  unit 
area  of  core,  its  iron  heat  will  be  eight 
times  that  of  the  small  transformer,  or 
four  times  its  total  heat;  but  as  the 
cooling  surface  is  only  four  times  as 


74 

great,  the  anomalous  result  follows,  that 
the  output  of  the  large  transformer  is 
zero,  although  its  electromotive  force 
would  be  four  times  that  of  the  other. 
The  comparison  would  have  been  still 
more  unfavorable  to  the  large  trans- 
former, had  it  been  assumed  that  the 
iron  heat  in  the  small  transformer  was 
greater  than  its  copper  heat.  Therefore 
in  order  to  be  able  to  work  the  large 
transformer  at  all,  the  induction  must  be 
reduced ;  that  is  to  say,  the  transformer 
used  on  a  circuit,  the  electromotive  force 
of  which  is  less  than  four  times  that  of 
the  small  transformer.  The  resistance 
of  the  large  coil  is  half  that  of  the  small 
one,  and  if  the  large  transformer  is 
worked  so  as  to  have  equal  iron  and 
copper  heat,  the  latter  may  obviously  be 
four  times  that  of  the  small  transformer; 
this  gives  a  current  2.82  times  the  value 
of  that  in  the  small  transformer.  The 
weight  of  iron  in  the  large  transformer 
being  eight  times  that  of  the  small  one, 
the  loss  by  hysteresis  per  unit  of  weight 
must  be  half.  The  corresponding  indue- 


75 

tion  can  be  ascertained  from  the  table. 
If,  for  instance,  the  induction  in  the 
small  transformer  is  8,000,  that  in  the 
large  one  may  be  taken  as  5,000,  and  the 

electromotive  force  will  be     '  AA  X  4  = 

o,UUU 

2.5  times  that  of  the  small  transformer,  the 
output  being  increased  in  the  ratio  of  1 
to  2.82  x  2.5  =  7  about.  It  should 
also  be  observed  that  the  larger  appa- 
ratus will,  in  so  far,  be  more  advantageous, 
as  a  smaller  proportion  of  space  will  be 
occupied  by  insulation,  especially  if  both 
are  required  for  the  same  circuit.  The 
ratio  of  output  may  thus  be  increased 
from  seven  to  eight,  or  ten,  or  even  more, 
according  to  the  size  of  transformer 
taken  as  the  basis  of  the  comparison. 
For  larger  sizes,  the  advantage  resulting 
from  an  increase  of  linear  dimensions 
will  be  less  apparent,  and  the  output  may 
roughly  be  taken  as  proportional  to  the 
weight. 

The  question  of  frequency,  alluded  to 
in  connection  with  alternators,  is  also  of 
considerable  practical  importance  with 


76 


regard  to  the  transformers,  and  it  is 
much  to  be  desired  that  electrical  engi- 
neers should  adopt  a  common  standard. 
Comparing  two  equal  transformers,  one 
working  with  a  frequency  of,  say,  65,  and 
the  other  with  one  of,  say,  130,  it  is 
evident  that  with  the  same  pressure  the 
induction  in  the  latter  need  only  be  half 
that  in  the  former ;  and  if  the  effect  of 
static  hysteresis  only  had  to  be  con- 
sidered, the  heat  generated  per  cycle 
would  be  something  less  than  half ;  and 
the  total  heat  generated  in  a  given  time 
would,  with  the  high  frequency,  be  some- 
what less  than  with  the  low  frequency. 
But  as  there  is  every  reason  to  believe  in 
the  existence  of  viscous  hysteresis,  by 
virtue  of  which  the  heat  generated  per 
cycle  increases  with  the  speed  at  which 
the  cycle  is  performed,  there  must  be  a 
limit  to  the  frequency  beyond  which  a 
further  increase  becomes  disadvantage- 
ous. With  the  present  imperfect  knowl- 
edge of  this  subject,  it  is  not  possible 
to  determine  this  limit  on  theoretical 
grounds ;  but  it  is  justifiable  to  look  to 


77 

common  practice  for  an  indication  of 
what  the  limit  probably  is.  The  present 
types  of  alternators  and  transformers,  it 
must  be  remembered,  are  not  mere 
experimental  machines,  but  the  survival 
of  the  fittest,  and  it  would  be  futile  to 
ignore  the  lessons  taught  by  practical 
experience  extending  over  several  years. 
The  following  is  a  list  giving  the  average 
frequencies  adopted  by  several  designers : 
Ferranti,  67  ;  Lowrie-Parker,  88 ;  Mor- 
dey,  100 ;  Zipernowsky,  42 ;  Kennedy, 
60  ;  Kapp,  80  ;  Westinghouse,  133. 

Taking  the  average  of  European  prac- 
tice, the  frequency  is  73,  or  8,750  reversals 
per  minute  ;  whilst  the  American  practice 
is  16,000  reversals  per  minute.  This 
large  difference  may,  to  a  certain  extent, 
be  accounted  for  by  the  general  pre- 
ference of  European  engineers  for 
machines  running  at  moderate  speeds: 
but  even  when  making  due  allowance  for 
this  circumstance,  it  can  hardly  be  as- 
sumed that,  had  actual  practice  shown 
the  value  of  a  very  high  frequency,  elec- 
trical engineers  would  not  have  found 


78 

means  to  obtain  it.  As  a  matter  of  fact, 
most  makers  of  alternators  have  started 
with  a  very  much  higher  frequency  than 
they  have  finally  adopted.  It  should 
also  be  remembered  that  the  higher  the 
frequency,  the  greater  is  the  loss  of  con- 
ductivity in  the  mains,  owing  to  the 
unequal  distribution  of  current  through- 
out their  cross-section. 

MOTORS. 

Machines,  for  the  conversion  of  the 
electrical  energy  of  alternating  currents 
into  mechanical  energy,  have  not  yet 
been  brought  to  such  a  state  of  perfec- 
tion that  the  problem  may  be  considered 
as  solved — and,  in  fact,  very  little  is  at 
present  known  as  to  the  details  of  such 
machines  and  the  results  achieved.  Mo- 
tive power  may  be  obtained  from  an 
alternating  current  in  either  of  three  dis- 
tinct methods : 

1.  By  the  employment  of  an  alternator 
with  separately  excited  field,  and  some 
means  to  first  run  it  up  to  speed  before 
switching  the  current  on.  Various  de- 


79 

vices  have  been  patented  for  this  method 
of  working ;  but  the  author  is  not  aware 
that  any  one  of  them  has  proved  success- 
ful. 

2.  By  the  employment  of  a  direct-cur- 
rent motor  with  laminated  field-magnets. 
Such  motors  have  been  made  and  tested 
by  various  engineers ;  and  about  two 
years  ago  the  author  also  experimented 
with  such  a  motor,  but  the  results  were 
discouraging.  The  work  obtainable  from 
this  motor,  with  a  given  current  and 
electromotive  force,  was  only  about  one- 
fifth  part  that  which  might  be  obtained 
from  the  same  motor  if  driven  by  a  direct- 
current  of  the  same  measured  strength, 
and  flowing  under  the  same  pressure. 
This  particular  type  of  motor  was,  there- 
fore, commercially,  quite  unfit  for  use 
with  an  alternating-current  supply.  After- 
wards, when  investigating  the  reason  of 
this  failure,  the  author  found  that  the 
electromotive  force  of  self-induction  was 
far  too  great,  in  comparison  to  the  counter 
electromotive  force  of  the  armature,  pro- 
ducing thus  a  very  large  lag,  and  conse- 


80 

quently  reducing  the  plant-efficiency  too 
much.  The  investigation  also  showed 
that,  under  the  most  favorable  conditions, 
the  plant- efficiency  of  such  a  motor  could 
not  be  more  than  70  per  cent.  This 
figure  would  be  obtained  if  the  electro- 
motive force  of  self-induction  of  the  whole 
machine  were  by  some  means  reduced,  so 
much  as  to  be  only  equal  to  the  counter 
electromotive  force  developed  in  the 
armature,  a  condition  which  is  extremely 
difficult,  if  not  impossible,  to  fulfill  in 
practice.  For  this  reason,  it  would  seem 
that  a  motor  of  this  type  must  always  be 
very  much  larger,  more  costly,  and  heavier 
than  a  direct-current  motor  of  the  same 
power.  It  has  the  advantage  of  being 
self -starting,  and  not  requiring  any  ac- 
cessory apparatus  for  its  excitation  or 
regulation.  On  the  other  hand,  there  is 
the  liability  of  the  armature  burning  up, 
if  the  motor  should  fail  to  overcome  its 
load  almost  at  once.  When  the  armature 
is  at  rest,  and  an  alternating  current 
passes  through  the  machine,  those  arma- 
ture coils  which  at  the  time  happen  to  be 


81 

short- circuited  by  the  brushes,  are  in  the 
same  condition  as  the  secondary  of  a 
transformer  short-circuited  upon  itself. 
They  will  therefore  be  liable  to  burn  up 
if  the  armature  cannot  start  at  once. 

3.  The  third  method  of  producing 
motive  power  from  alternating  currents 
has  hitherto  received  most  attention,  as 
being  the  most  promising.  It  is  due  to 
a  discovery  made  about  a  year  and  a  half 
ago  by  Professor  Galileo  Ferraris,  of 
Turin.  This  scientist  found  that  a  cop- 
per cylinder,  suspended  between  two 
coils,  was  set  into  rotation  if  alternating 
currents  of  the  same  period,  but  of  differ- 
ent phase,  were  sent  through  these  coils 
which  were  placed  at  right  angles  to  each 
other.  The  explanation,  given  by  Pro- 
fessor Ferraris,  was  that  the  resultant 
field  of  the  two  currents  revolved  round 
the  common  center-line  of  the  coils,  and, 
by  means  of  eddy  currents  created  in  the 
copper  cylinder,  dragged  the  latter  after 
it.  This  principle  has  been  practically 
developed  by  Mr.  Nicola  Tesla  and  others, 
and  motors  have  been  actually  built  in 


82 


which  a  revolving  field  causes,  by  a  kind 
of  electro-magnetic  drag,  an  armature  to 
revolve  and  give  off  mechanical  work. 
This  action  may  be  represented  by  the 
diagram  Fig.  12,  where  A  A  and  B  B  are 
two  coils  placed  at  right  angles,  and  in 


the  common  center,  O,  of  which  is  placed 
an  armature  consisting  of  a  series  of  coils 
C,  each  forming  a  loop  closed  on  itself. 
Let  there  be  a  difference  of  phase  of  90° 
between  the  currents  in  the  two  field- 


83 

coils,  and  let  0  Fa  and  O  Fb  represent 
the  fields  produced  at  a  given  moment.  ^ 
The  resultant  field  is  O  F,  and  this 
revolves  round  O  with  a  speed  corre- 
sponding to  the  frequency.  In  the 
diagram  a  cross  placed  in  the  circle, 
representing  a  wire  or  coil,  signifies  an 
ascending,  and  a  dot  a  descending  cur- 
rent. When  the  rotation  of  the  resultant 
field  takes  place  in  the  direction  of  the 
arrow,  the  current  in  B  must  be  approach- 
ing zero,  and  that  in  A  its  maximum 
value. 

Suppose,  now,  the  armature  is  held  at 
rest.  The  field  in  sweeping  through  the 
conductors  C  induces  in  them  currents  in 
the  direction  indicated,  and  the  latter 
therefore  exert  a  torque.  Imagine  the 
field  stationary,  and  the  armature  re- 
volved by  a  belt.  In  this  case,  the  cur- 
rent created  in  the  short-circuited  coils 
will  produce  a  torque  tending  to  resist 
rotation.  The  lower  the  resistance  of 
these  coils  and  the  greater  the  speed  of 
rotation,  the  more  power  will  be  required 
to  rotate  the  armature.  It  is  thus  evident 


84 

that  with  a  revolving  field  the  greatest 
force  will  be  exerted  upon  the  armature 
<  whilst  this  is  at  rest,  and  that  the  power 
will  decrease  as  the  armature  begins  to 
revolve  and  gather  speed,  just  as  in  an 
ordinary  direct-current  motor.  When 
the  speed  of  the  armature  coincides  with 
that  of  the  resultant  field,  no  torque  is 
produced,  whilst  at  starting,  the  torque 
is  a  maximum.  According  to  the  load 
put  upon  the  motor,  the  armature  will 
therefore  automatically  assume  that  speed 
which  corresponds  to  the  load,  and  in 
this  respect  the  condition  of  working  is 
comparable  to  that  of  a  continuous- cur- 
rent motor.  The  current  through  the 
armature  coils  C  produces  a  field,  O/> 
which  is  also  revolving,  and  in  sweep- 
ing past  the  wires  in  the  fixed  coils  A  A, 
B  B,  creates  therein  an  electromotive 
force  which  is  always  opposing  the  flow  of 
current,  as  will  easily  be  seen  from  the 
diagram.  It  will  also  be  observed  that 
the  wave  of  counter  electromotive  force 
in  the  fixed  coils,  thus  produced,  coin- 
cides with  the  current  wave  therein,  and 


85 

the  current  must  therefore  do  work  in 
flowing  against  this  counter  electromotive 
force.  It  is  this  work  thus  absorbed  by 
the  fixed  coils  which  partly  reappears  as 
mechanical  work  of  rotation  given  out  by 
the  armature,  the  rest  being  dissipated 
in  heat  as  in  the  case  of  an  ordinary 
motor.  The  action  here  explained  is  in 
reality  not  quite  so  simple,  because  self- 
induction  and  the  reaction  of  the  arma- 
ture field  have  to  be  taken  into  account ; 
but,  in  the  absence  of  all  experimental 
data,  it  is  not  worth  while  to  attempt  a 
closer  investigation.  The  author  has 
thought  it  expedient  to  explain  the  funda- 
mental principle  of  this  type  of  motor,  as 
the  investigation  might  prove  useful  to 
those  who  are  about  to  experiment  with 
similar  machines.  He  regrets  that  he  is 
unable  to  place  before  the  institution 
details  of  the  Tesla  motor,  as  constructed 
by  the  Westinghouse  company ;  but  as 
these  details  are  only  partially  worked 
out,  and  secured  by  patents,  this  com- 
pany naturally  prefer  to  withhold  them 
for  the  present. 


86 

DESCRIPTION  or  MODERN  ALTERNATORS. 

By  the  courtesy  of  the  designers  and 
makers  of  alternators,  the  author  is  able 
to  submit  particulars  of  the  various 
machines  most  in  use,  and  he  takes  this 
opportunity  of  tendering  his  thanks  to 
those  who  have  supplied  him  with  infor- 
mation. Modern  alternators  may  be 
divided  into  two  classes,  disk  machines 
and  drum  machines.  In  the  former  type 
the  armature-coils  are  arranged  in  disk 
form,  and  the  magnet- poles  are  presented 
to  them  from  two. sides,  whilst  in  the 
latter  type  the  coils  are  arranged  to  form 
a  cylindrical  surface,  and  the  magnet- 
poles  are  presented  from  one  side  only. 

DISK   MACHINES. 

THE  FERRANTI  ALTERNATOR. 

The  magnet-cores  are  of  trapezoidal 
section  (Figs  13  and  14),  and  supported 
in  cast-iron  yoke- rings.  The  armature- 
conductor  is  a  thin  corrugated  copper 
strip,  wound  with  a  strip  of  vulcanized 
fiber  of  equal  width  upon  a  brass  core. 


87 

To  avoid  eddy  currents  in  the  latter,  it  is 
subdivided  into  corrugated  narrow  strips, 
separated  from  each  other  by  asbestos. 


The  shape  of  the  coils  is  shown  in  Fig. 
13.  At  the  inner  and  narrower  end,  the 
core  is  provided  with  a  projection  by 
which  it  is  secured  to  a  bobbin-carrier. 


88 

This  in  turn  is  supported  by,  but  insu- 
lated from,  the  central  armature- ring. 
There  are  two  bobbins  to  each  carrier, 
which  forms  the  metallic  connection  be- 
tween their  inner  ends.  There  is  thus  a 
double  insulation  for  the  coil,  first  that 
of  the  conductor  against  the  core  and 
bobbin-carrier ;  and  secondly,  that  of  the 
latter  against  the  body  of  the  machine. 
The  winding  of  the  coils  is  such,  that  the 
current  passes  through  the  armature  in 
two  parallel  circuits,  by  which  arrange- 
ment the  terminals  of  the  armature  are 
brought  to  opposite  points  of  a  diameter ; 
and  the  connection  between  adjacent 
coils  is  made  automatically,  by  the  act  of 
inserting  and  bolting  up  the  coil  so  that 
it  is  impossible  for  a  workman,  when 
replacing  a  coil,  to  make  a  wrong  con- 
nection. The  mean  width  of  poles  is 
approximately  equal  to  half  the  pitch,  and 
the  width  of  coils  is  also  equal  to  half  the 
pitch,  so  that,  according  to  the  table  on 
p.  22,  the  coefficient  is  2.300.  The  follow- 
ing are  the  principal  data  for  a  150-HP. 
machine:  500  revolutions,  46.5  amperes, 


89 

2,400  volts,  20  poles.  Armature-conductor 
490  by  11.8  mils.  Current  density  4,000 
amperes  per  square  inch.  Eesistance  of 
armature  1.2  ohm.  Total  number  of  con- 
ductors on  armature  3,440,  divided  into 
two  parallels  of  1,720  each.  Field-coils  of 
320  turns,  exciting  current  13.5  amperes. 
Exciting  power  17,200  ampere  turns. 
The  interpolar  space  is  0.75  inch,  and  the 
area  of  pole-pieces  14.5  square  inches. 
From  these  data  it  is  possible  to  calculate 
the  total  flow  of  the  lines.  It  is  in 
English  measure  z  —  130,  and  the  elec- 
tromotive force  of  an  equivalent  con- 
tinuous current  machine  would  be  1,150 
volts.  The  ratio  between  this  figure  and 
the  electromotive  force  of  the  alternator  is 
2.15  which  agrees  fairly  well  with  the  theo- 
retical value  of  2.30  mentioned  above. 
The  resistance  of  the  field  is  12.8  ohms, 
and  the  exciting  energy  2,340  watts,  or 
only  2.3  per  cent,  of  the  total  output. 

THE  MORDEY  ALTEKNATOR. 

This  is  also  a  disk  machine;  but  with 
revolving   magnets   and  Jixed   armature 


90 

(Figs.  15  and  16).  The  cores  of  the  arma- 
ture-coils are  of  porcelain,  and  the  con- 
ductor consists,  as  in  the  Ferranti  ma- 
chine, of  a  thin  copper  strip  insulated  in 
a  similar  manner.  The  distinguishing 
feature  of  this  machine  is  the  field.  It 
is  of  the  iron-clad  description,  and  the 
poles  on  one  side  are  all  of  the  same 
sign,  whilst  those  on  the  other  side  of  the 

Fig.  15  Fig.  16 


armature  are  of  the  opposite  sign.  There 
is  only  one  coil  of  exciting  wire,  C,  placed 
as  shown  in  the  diagram.  The  field  may 
be  diagrammatically  represented  by  Fig. 
£.  Each  group  of  conductors  is  fairly 
concentrated,  and  the  coefficient  k  for 
ihis  machine  should,  therefore,  lie  be- 
iween  the  values  given  for  cases  1  and  3 
on  p.  22.  If  the  conductors  were  con 


91 

centrated  into  lines,  k  would  be  equal  to 
2  000 ;  if  they  occupied  half  the  available 
space,  it  would  be  1.635.  As  will  be 
seen  from  the  diagram,  they  occupy 
rather  less  than  half  the  available  space, 
and  k  should,  therefore,  be  greater  than 
1.635,  though  smaller  than  2.  The 
author  has  not  been  able  to  obtain  the 
constructive  data  of  this  machine,  and 
can,  therefore,  not  give  the  exact  value 
of  the  coefficient  k  for  it. 

THE  KENNEDY  ALTERNATOE. 
This,  too,  is  a  disk  machine  of  the  iron- 
clad type,  the  field  being  stationary  and 
the  armature  revolving  (Figs.  17,  18,  and 
19).  The  latter  has  an  iron  core,  A, 
round  which  the  armature-conductor  is 
wound,  forming  radial  coils  with  parallel 
sides.  The  field-magnet  consists  of  an 
external  yoke-ring  y  bounded  by  flat 
annular  disks,  which  on  their  inner  faces 
are  provided  with  polar  projections  N  S, 
occupying  relatively  to  each  other  inter- 
mediate angular  positions.  There  is  only 
one  coil  of  exciting  wire,  which  is,  how- 


92 

ever,  for  greater  convenience  of  manufact- 
ure, arranged  in  two  halves,  C  C.  Fig. 
19  shows  diagrammatically  the  relative 
position  of  armature-coils  and  field-poles 
straightened  out.  It  will  be  seen  that 
the  lines  of  force,  which  are  shown  dotted, 
have  an  oblique  course,  and  that  only 
one-half  of  the  wire  in  the  armature- coil 
is  at  any  time  in  the  position  of  greatest 
activity.  The  width  of  the  field,  when 
making  due  allowance  for  the  fringe  of 
lines  which  surrounds  the  actual  contour 
of  the  pole-piece,  is  somewhat  greater 
than  the  pitch ;  whilst  the  proportion  of 
space  on  the  armature,  occupied  by  the 
winding,  varies  with  the  radial  distance 
at  which  it  is  measured.  On  the  inside 
of  the  armature  nearly  the  whole  space 
is  so  filled,  whilst  on  the  outside  a  little 
less  than  half  the  space  is  occupied  by 
the  coils.  For  the  outside  of  the  arma- 
ture the  coefficient  k  will,  therefore,  be 
nearly  that  corresponding  to  case  3  on 
p.  22,  and  for  the  inside  it  will  be  rather 
less  than  that  of  case  2.  The  actual 
mean  value  of  the  coefficient  should 


93 

therefore  be  a  little  greater  than  1.000 ; 
and  this  is,  indeed,  the  case.  According 
to  a  calculation  made  by  Mr.  Kennedy, 
the  number  of  English  lines  emanating 
from  one  pole  is,  for  the  machine  illus- 
trated in  the  diagram,  148  ;  the  armature 
contains  twelve  coils  of  18  turns  each,  or 
216  turns  in  all ;  the  exciting-coils  con- 
Fig.  17  Fig;  18 


tain  570  turns  of  wire,  the  exciting-current 
is  25  amperes,  and  the  exciting-power  is, 
therefore,  14,250  ampere  turns.  At  a 
speed  of  800  revolutions  per  minute,  the 
terminal  pressure  is  150  volts,  and  the 
current  70  amperes,  the  output  being 
thus  10.5  kilowatts.  No  experiments 
have  been  made  to  determine  the  induced 
electromotive  power,  which  naturally  is- 


94 

effected  by  the  self-induction  of  the 
armature;  but  Mr.  Kennedy  states  that 
the  difference  in  exciting-power  for  full 
output  and  running  idle  is  not  great. 
From  analogy,  with  his  own  machines, 
the  author  estimates  that  the  induced 
electromotive  force  of  this  machine,  when 
giving  150  volts  at  the  terminals,  would 
be  about  165  volts.  If  the  armature  were 
coupled  to  give  a  continuous  current,  the 
electromotive  force  produced  by  a  field 
of  148  lines  would  be  154,  so  that  k  in 
this  machine  must  be  about  1.07.  This 
yalue,  although  rather  smaller  than 
theory  would  indicate,  is  yet  within  the 
limits  given  above.  It  may  here  be 
mentioned  that  Mr.  Kennedy  advocates 
the  use  of  low-pressure  alternators  in 
connection  with  step-up  transformers  if 
a  high-pressure  current  is  required. 

THE   KAPP   ALTERNATOR. 

The  author's  machine  is  illustrated  in 
Figs.  20  and  21.  The  armature-core  A 
consists  of  thin  band-iron  coiled  upon 
a  cast-iron  supporting-ring,  and  sur- 


95 

rounded  by  radial  coils  c.  The  yoke- 
rings  y  are  of  cast-iron  and  the  magnet- 
cores  of  wrought  or  cast-iron  with  pole- 
shoes  of  rectangular  shape.  This  arrange- 
ment has  been  adopted  with  a  view  to 
obtain,  on  the  outside  of  the  armature,  as 
large  a  ratio  as  possible  between  the 
pitch  and  length  of  field.  For  the  same 
purpose,  and  to  reduce  leakage,  the  pole- 
shoes  are  tapered  on  the  inside.  The 
importance  of  securely  supporting  the 
armature-wires  is  well  known,  and  there 
is  hardly  any  good  continuous-current 
dynamo  now  made,  in  which  this 
mechanical  detail  does  not  receive  careful 
attention.  In  alternators,  a  strong 
mechanical  fastening  of  the  wires  on  the 
armature  is,  however,  of  even  greater 
importance.  The  mechanical  strain  to 
which  the  wire  is  subjected  depends,  not 
on  the  mean  current  and  electromotive 
force  at  which  the  machine  is  rated,  but 
on  their  maximum  values.  Now  the 
maximum  value  of  the  periodic  current 
is  about  40  per  cent,  greater  than  the 
mean  value,  and  the  same  is  the  case  with 


96 

the  electromotive  force.  It  should  also 
be  observed  that  the  strain  depends  upon 
the  induced  electromotive  force,  whereas 
the  output  is  computed  on  the  basis  of 
the  terminal  electromotive  force,  which  is 
somewhat  smaller.  As  the  crest  of 
the  current- wave  occurs  in  ordinary 
work  only  a  very  short  time  after  that 
of  induced  electromotive  force,  the 
mechanical  strain  to  which  each  coil  is 
subjected  twice  in  each  period  is  that 
due  to  the  maxima,  and  not  to  the 
mean  values  of  current  and  electromotive 
force,  and  is  therefore,  roughly  speaking, 
at  least  twice  as  great  as  in  a  continuous- 
current  machine  of  the  same  dimensions 
and  output.  To  provide  against  these 
strains,  the  author  inserts  between  the 
coils  driving-horns  of  insulated  metal  or 
fiber,  which  pass  through  the  core  of  the 
armature,  and  are  secured  in  their  posi- 
tion by  radial  bolts.  The  machine 
illustrated  in  Figs.  20  and  21  is  one  of  five 
120-kilowatt  alternators  now  in  course 
of  construction  for  a  central  station ; 
but  as  it  has  not  yet  been  tested,  it  will 


97 


be  more  satisfactory  to  give  the  construct- 
ive data  and  results  of  a  smaller  machine 
which  has  been  at  work.  For  this  pur- 
pose may  be  selected  the  machine  to 
which  the  characteristic  curves,  Fig.  11, 
refer,  and  which  has  been  exhaustively 
tested  by  Mr.  Brown,  as  already  men- 
tioned. The  supporting-ring  of  this 
machine  is  31  inches  in  diameter  and  3 
inches  wide.  The  core  is  of  equal  width 


Fig.  21 


and  8 1  inches  deep,  and  is  wound  with 
1,120  turns  of  wire  arranged  in  fourteen 
coils  of  80  turns  each.  The  resistance  of 
the  armature  when  warm  is  1.74  ohm. 
The  field-magnet  cores  are  of  cast  iron,  3 
inches  by  7  inches,  with  rounded  corners, 
and  there  are  no  pole-shoes.  Each  mag- 
net-coil contains  140  turns  of  wire,  and 
the  total  resistance  of  the  twenty-eight 
coils  is  1.73  ohm.  The  calculated 


98 

strength  of  field  at  6,000  ampere  turns  is 
142  English  lines,  and  the  observed 
terminal  pressure  when  running  idle  is 
1,560  volts.  This  gives  a  coefficient  of  k 
=  2.370.  When  working  at  the  full  out- 
put of  30  amperes  and  2,000  volts,  the 
mean  electromotive  force  of  self  induction 
is  1,250  volts,  and  the  induced  electromo- 
tive force  2,400  volts.  The  loss  of  press- 
ure through  armature-resistance  is  in  that 
case  52  volts,  or  about  2.6  per  cent,  of 
the  terminal  electromotive  force.  The 
energy  lost  in  exciting  the  field,  which 
requires  12,000  ampere  turns,  is  3.2 
kilowatts,  or  5.3  per  cent,  of  the  output. 
This  somewhat  large  percentage  is  due  to 
the  employment  of  cast  iron  for  the  mag- 
net-cores, and  will,  in  the  machine  illus- 
trated, which  has  cylindrical  magnets  of 
wrought-iron,  be  reduced  to  about  3.5 
per  cent.  The  data,  obtained  by  Mr. 
Brown  in  testing  this  machine,  suffice  for 
the  determination  of  the  coefficient  of 
self-induction  by  means  of  a  diagram 
similar  to  Fig.  7,  which  also  gives  the 
angle  of  lag.  Knowing  the  latter,  it  is 


99 

possible  to  find  the  counter-magnetomo- 
tive force  due  to  the  armature  current  at 
the  moment  when  the  armature-coils  are 
in  mid  position  between  two  poles.  The 
maximum  current  is  30  ^/  2  =  42.4  am- 
peres, and  the  corresponding  exciting 
power  is  3,400  ampere  turns.  This, 
however,  occurs  at  a  time  when  the  coils 
are  well  within  the  polar  surfaces  of  the 
field-magnets  and  the  poles  produced  in 
the  armature  are  between  neighboring 
field-poles.  In  this  position  the  demag- 
netizing effect  must  be  naturally  small. 
It  will  be  a  maximum  when  the  armature- 
poles  are  opposite  the  field-poles,  and  at 
that  moment  the  exciting  power  of  the 
armature-current  is  about  1,700  ampere 
turns.  This  value  must,  therefore,  be 
deducted  from  the  exciting  power  applied 
to  the  field,  to  obtain  the  true  effective 
exciting  power  which  is  causing  the  flow 
of  lines.  Thus  the  value  10,300  is  ob- 
tained, to  which  corresponds  a  flow  of 
215  lines  through  the  armature,  giving 
the  induced  electromotive  force  of  2,400 
volts. 


100 

DRUM    MACHINES. 

The  distinctive  feature  of  the  machines 
comprised  under  this  title  is  that  the 
armature-coils  do  not  surround  the  core, 
but  are  arranged  on  one  side  of  it.  As 
examples,  may  be  mentioned  the  Westing- 
house,  the  Lowrie-Parker,  and  the 
Zipernowsky  machines. 


THE    WESTINGHOUSE    ALTERNATOR. 

The  armature-core  of  this  machine  is 
of  cylindrical  shape,  and  consists  of  thin 
iron  plates,  as  in  an  ordinary  drum  machine 
for  continuous  currents.  To  provide 
internal  cooling  surfaces,  the  plates  have 
large  holes  cut  out  of  their  surface,  form- 
ing, when  put  together,  tunnels,  going 
from  end  to  end,  through  which  the  air 


101 

may  circulate.  The  armature-coils  are 
of  flat-link  shape  with  rounded  ends, 
which  are  laid  on  to  the  surface  of  the 
core  with  the  active  wires  parallel  to  the 
spindle.  The  ends  of  the  coils  are 
brought  over  the  end  plates  of  the  core, 
and  bent  inwards,  as  shown  at  C  C  C  in 
Fig.  22,  and  secured  in  that  position. 
The  straight  portions  of  the  coils  are 
fastened  to  the  surface  of  the  core  by 
insulated  filling-pieces  and  binding-hoops. 
The  field  magnets  N  S  are  set  radially 
outside  the  armature,  and  their  outer  ends 
are  connected  by  a  cylindrical  yoke  y. 

THE  LOWRIE-PARKER  ALTERNATOR. 

This  machine  is  the  inverse  of  that 
just  described.  The  armature  is  outside 
of  the  field,  and  is  stationary,  whilst  the 
magnets  revolve.  The  armature  coils 
C  0,  Fig.  23,  are  also  of  flat-link  shape, 
the  conductor  consisting  of  a  cotton- 
covered  strip,  wound  upon  a  core  of  wood 
with  rounded  ends ;  they  are  laid  with 
their  long  side  parallel  to  the  spindle  on 
to  the  inner  surface  of  the  armature-core 


102 

A,  which  is  built  up  of  segmental  plates 
to  form  a  cylinder.  The  following  par- 
ticulars refer  to  a  100-kilowatt  machine, 
giving  50  amperes  at  2,000  volts  terminal 
pressure,  the  speed  being  380  revolutions 
per  minute.  The  internal  diameter  of  the 
armature  core  is  5  feet  1  inch ;  the  radi- 
al depth  5  inches,  and  the  length  14 


Fig.  23 


inches.  There  are  twenty-eight  coils, 
each  containing  21  turns,  so  that  the 
total  number  of  active  wires,  counted  all 
round,  is  eleven  hundred  and  seventy- six. 
The  field-magnet  cores  are  of  wrought- 
iron,  3  inches  by  13^  inches,  and  are 
bolted  to  a  wrought-iron  yoke-ring  y. 
Each  magnet-coil  contains  130  turns  of 


103 

exciting  wire,  and  the  exciting  current  is 
28  amperes.  This  gives  an  exciting 
power  of  7,300  ampere  turns,  and  the 
calculated  strength  of  field  is  144  English 
lines.  Allowing  for  self-induction  and 
resistance,  the  induced  electromotive 
force  may  be  taken  as  2,050  volts.  A 
continuous-current  machine  of  the  same 
dimensions  and  winding  would  give  900 
volts ;  so  that  for  this  machine,  as 
arranged  to  produce  an  alternating  car- 
rent,  the  coefficient  is  k  =  2.280.  The 
width  of  the  field,  allowing  for  the  fringe 
of  lines  round  the  pole  pieces,  is  0.55  of 
the  pitch,  and  the  surface  covered  by  the 
active  wires  in  the  armature-coils  is  0.55 
of  the  whole  surface.  Theory  would  there- 
fore indicate  that  the  coefficient  must  be 
very  nearly  that  given  for  case  5,  p.  22, 
namely,  2.300,  which  is  indeed  the  case. 
In  a  150-kilowatt  machine  of  the  same 
type,  the  output  is  75  amperes  at  2,000 
volts  pressure ;  the  speed  being  500 
revolutions  per  minute,  and  the  frequency 
100.  There  are  twenty-four  poles,  and 
the  number  of  active  wires  is  six  hun- 


104 

dred  .and  twenty- four.  Resistance  of 
armature,  0.32  ohm,  and  that  of  the 
magnets  25  ohms ;  exciting  current,  15 
amperes. 


THE    PARSONS   ALTERNATOR. 
This   machine,  of  which  Fig.   24  is  a 


105 

section,  and  Fig.  25  an  elevation,  is  a 
modification  of  the  well-known  turbo- 
electric  generator  of  the  Hon.  Charles 
Parsons.  It  is  the  only  example  of  a 
bi-polar  alternator  with  drum  arma- 
ture, the  arrangement  being  inter- 
mediate between  that  shown  in  Fig.  4  and 
Fig.  5,  that  is  to  say  the  polar  surfaces, 
although  not  completely  surrounding  the 
armature,  yet  embrace  more  than  half 
the  circumference.  The  armature  core 
consists  of  thin  iron  plates  insulated 
with  paper  and  mica,  and  threaded  upon 
the  spindle.  The  wire  is  laid  on  in  a 
single-coil,  the  ends  being  brought  to 
two  collecting  rings  in  the  usual  way. 
In  a  75-kilowatt  alternator,  giving  75 
amperes  at  1,000  volts  terminal  pressure, 
the  armature  core  is  7  inches  in  diameter 
by  30  inches  long,  and  the  core  of  the 
field-magnets,  which  are  of  cast-iron,  is  5 
inches  by  28  inches.  The  armature  coil 
contains  one  hundred  and  ten  active 
wires,  127  millimeters  in  diameter,  giving 
a  current-density  of  6,000  amperes  per 
square  inch.  The  armature  resistance  is 


106 

0.22  ohm,  and  the  loss  1.65  per  cent,  of 
the  output.  The  speed  of  this  machine 
is  6,000  revolutions  a  minute,  giving  a 
frequency  of  n  =  100.  The  armature 
weighs  360  Ibs.,  and  the  weight  of  the 
complete  machine,  including  the  turbo- 
motor,  is  about  2  tons. 

THE  ZIPERNOWSKY  ALTERNATOR. 

This  machine  is  very  similar  to  the  one 
just  described,  the  principal  difference 
being  that,  instead  of  a  smooth  core,  the 
armature  is  provided  with  a  core  having 
Pacinotti  projections  on  the  inside.  The 
magnet  cores  N  S,  Fig.  26,  are  composed 
of  U-shaped  iron  plates,  to  avoid  the  heat- 
ing which  would  otherwise  result  from 
the  employment  of  an  armature  with  pro- 
jections. The  core  of  the  armature  is 
formed  of  thin  sheet-iron  segments  A, 
each  resembling  a  very  short  or  shallow 
T,  the  armature- coil  C  being  placed  over 
the  central  stem  of  the  T.  Each  arma- 
ture-segment with  its  coil  forms  a  sepa- 
rate part,  which  can  be  inserted  or  with- 
drawn without  disturbing  the  rest  of  the 


107 

machine.  This  is  a  great  practical  ad- 
vantage, because  facilitating  repairs. 
There  is  a  slight  increase  in  magnetic 
resistance  due  to  the  want  of  continuity 
of  armature-core ,  but,  as  the  interpolar 
space  can  be  made  very  small,  the 
increase  of  magnetic  resistance  in  the 
armature-core  is  permissible. 


Fig.  26 


ZIPERNOWSKY 


The  following  particulars  refer  to  a 
machine  giving  40  amperes  at  2,000  volts 
terminal  pressure,  or  80  kilowatts  output. 
There  are  fourteen  poles  in  the  field,  and 
fourteen  coils  in  the  armature.  The 
speed  is  360  revolutions  per  minute,  and 
the  frequency  is  n  =  42.  The  weight  of 
laminated  iron  in  field  and  armature  col- 


108 

lectively  is  1  ton  7  cwt.,  and  that  of 
copper  in  the  armature  and  field- coils 
collectively  is  930  Ibs.  The  armature 
resistance  is  1.038  ohm,  and  that  of  the 
field  coils  is  3.24  ohms  ;  exciting  current, 
28.7  amperes.  The  loss  of  energy  in  the 
armature  is  thus  2.08  per  cent.,  and  that 
in  the  field  3.33  per  cent,  of  the  output. 
Some  experiments  were  made  with  this 
machine  to  determine  the  loss  due  to 
windage,  mechanical  friction,  and  mag- 
netic friction.  For  this  purpose  the 
machine  was  driven  by  a  belt  from  an 
electromotor,  the  efficiency  of  which  had 
previously  been  determined.  For  the 
first  experiment,  the  field  of  the  alterna- 
tor was  not  excited,  and  the  power 
required  to  drive  it,  at  its  normal  speed 
of  360  revolutions  per  minute,  was  found 
to  be  4.07  HP.  In  the  next  experiment 
the  field  was  excited  so  as  to  produce  a 
terminal  pressure  of  2,000  volts  ;  but  no 
current  was  allowed  to  fiow  through  the 
armature,  and  the  power  required  was 
found  to  be  9.81  HP.  From  these 
experiments  it  appears  that  the  loss 


109 

through  magnetic  friction  was  5.74  HP. 
The  total  commercial  efficiency  at  full 
load,  when  the  alternator  is  driven  by  a 
belt,  and  inclusive  of  the  power  required 
for  exciting,  is  given  by  the  makers  as 
87  per  cent.  When  driven  direct  by  a 
high-speed  engine,  the  efficiency  is 
slightly  greater,  as  there  is  no  increase  of 
journal  friction  by  reason  of  the  strain  in 
the  belt. 


,      DISCUSSION. 

Sir  George  B.  Bruce,  President,  said 
the  paper  was  evidently  the  work  of  a 
perfect  master  of  the  subject  of  which  he 
treated,  and  he  was  sure  that  the  mem- 
bers would  award  the  author  a  vote  of 
thanks  for  so  valuable  a  contribution; 
nor  did  he  think  that  he  was  sanguine 
in  anticipating  that  it  would  give  rise  to 
a  very  important  discussion. 

Mr.  Gisbert  Kapp  was  afraid  the  mem- 
bers had  found  the  paper  somewhat  dry ; 
but  he  had  asked  several  friends  to 
enable  him  to  render  the  proceedings  a 
little  less  dry  by  lending  him  some  appa- 


110 

ratus.  Most  of  the  exhibits  were  new, 
and  were  then  shown  for  the  first  time. 
Amongst  the  transformers  was  Mr.  Mor- 
dey's,  consisting  of  rectangular  iron 
plates  and  bridge-pieces,  the  long  rect- 
angular coils  being  threaded  through 
the  cavities  thus  formed.  The  construc- 
tion was  very  simple.  The  metal  stamped 
out  of  the  rectangle  formed  a  bridge- 
piece,  thus  completing  the  magnetic  cir- 
cuit. The  transformers  were  built  up  in 
such  lengths  as  would  give  the  required 
pressure,  and  the  same  plates  were  used 
for  various  sizes.  If  half  the  pressure 
was  wanted,  half  the  number  of  plates 
were  used.  There  were  other  trans- 
formers exhibited,  two  by  Messrs.  Lowrie 
and  Hall,  which  were  used  in  Eastbourne, 
and  were  about  to  be  used  in  London, 
and  also  two  of  the  author's  type.  The 
core  of  the  Lowrie-Hall  transformer  was 
composed  of  iron  plates  insulated  with 
varnished  gauze,  and  brought  together 
over  the  ends,  where  they  were  protected 
by  iron  caps.  The  coils  were  wound  on 
both  limbs.  There  was  a  20-HP.  trans- 


Ill 

former  of  his  own  of  last  year's  pattern, 
made  by  Messrs.  Goolden  and  Co.,  and 
another,  the  latest  pattern,  made  by 
Messrs.  Johnson  and  Phillips.  The 
difference  between  them  was  that  one 
was  adapted  for  indoor  and  the  other  for 
outdoor  use.  They  could  act  under 
water,  and  had  been  so  worked  for  trial, 
but  of  course  no  one  would  think  of 
working  them  in  that  way  permanently. 
In  the  new  pattern  transformer  the  wind- 
ing was  split  up,  so  that  the  difference  of 
potential  of  any  particular  coil  would 
only  be  a  portion  of  the  total  pressure. 
The  arrangement  had  another  advantage, 
If  transformers  were  wanted  for  two- 
different  voltages,  say  50  or  100,  the 
same  instrument  could  be  used,  as  the 
two  secondary  coils  could  be  coupled  in 
parallel  for  the  lower  and  in  series  for 
the  higher  pressure.  Some  iron  tubes 
and  steel  boxes  were  shown,  as  used  by 
Messrs.  Lowrie  and  Hall  for  distribution 
by  underground  mains,  drawn  through 
these  tubes.  There  were  also  samples  of 
lead  cables,  the  joints  of  which  were 


112 

made  in  an  extremely  ingenious  way. 
The  lead  was  first  stripped  off,  and  the 
insulation  removed  over  a  distance  suffi- 
cient for  making  the  joint;  when  that 
had  been  done  the  insulation  was  re- 
placed, a  plate  of  lead  was  put  over  it, 
and  a  tool  like  a  pair  of  nippers  took  it 
round  and  squeezed  it  into  the  shape 
shown,  making  a  very  strong  joint.  The 
connections  were  made  in  the  boxes, 
which  were  of  three  different  types. 
Among  the  exhibits  was  one  of  Mr. 
Lowrie's  meters,  containing  a  secondary 
battery  in  series,  with  a  set  of  copper 
depositing  plates  and  the  consumers' 
main  leads.  It  did  not  measure  currents, 
but  conductivity-hours.  If  the  lamps 
were  switched  on,  but  no  alternate  cur- 
rent was  sent  through,  and  the  circuit 
was  simply  completed,  the  meter  regis- 
tered conductivity-hours ;  but  as  the 
pressure  was  always  on  the  mains,  that 
was  equivalent  to  registering  energy.  It 
had  been  in  use  for  two  years  with  good 
results.  There  was  also  an  ampere 
meter  for  alternate  currents.  The  cur- 


113 

rent  was  measured  by  the  heating  effect 
upon  compound  strips  of  metal.  The 
heat  caused  the  strips  to  deflect,  and  the 
motion  was  recorded  by  a  pointer.  There 
was  also  shown  a  safety  fuse  which 
would  be  melted,  and  thus  interrupt  the 
current  when  it  exceeded  a  predeter- 
mined limit.  With  a  pressure  of  2,000 
volts  it  was  necessary  to  have  a  long 
fuse-wire,  because  the  arc  set  up  upon 
the  melting  of  the  fuse  would  remain, 
unless  its  length  were  considerable.  As 
a  further  precaution  to  make  the  arc 
cease,  the  wire  itself  was  within  a  slot  in 
the  slate  base,  and  the  arc  was  thus  sub- 
jected to  the  chilling  effect  of  the  cold 
slate.  He  was  able  to  exhibit  a  portion 
of  a  switch  of  Mr.  Lowrie's  installation 
in  Kensington,  by  which  the  connection 
between  the  different  dynamos  and  cir- 
cuits could  be  effected.  Also  an  ex- 
tremely neat  arrangement  for  showing 
the  insulation  of  the  cables.  It  was 
nothing  more  than  a  Geissler  tube.  One 
pole  was  put  to  earth,  and  the  other  was 
put  to  any  one  of  the  circuits  which  were 


114 

to  be  tested.  If  the  insulation  was  good 
on  that  particular  circuit,  the  tube 
showed  a  bluish  light,  which  was  ob- 
served through  the  eye-hole.  If  it  was 
faulty,  this  static  effect  did  not  take 
place;  the  tube  remained  dark,  and  the 
attendant  knew  that  the  particular  main 
was  faulty,  and  must  be  repaired.  If 
complicated  tests  were  used,  requiring 
•elaborate  apparatus  which  could  not  be 
easily  carried  about,  the  men  would  be 
sure  to  neglect  it.  With  a  little  instru- 
ment like  that  exhibited,  two  or  three 
circuits  could  be  tested  in  half  a  minute. 
The  author  also  exhibited  an  armature- 
coil  of  one  of  Mr.  Mordey's  dynamos 
shown  in  Fig.  15  ;  also  various  measur- 
ing instruments,  a  safety  apparatus  in- 
vented by  Captain  Cardew,  and  various 
photographs  of  the  large  dynamos  made 
by  Mr.  Ferranti. 

Mr.  W.  H.  Preece  said  that  it  might 
not  be  out  of  place  if  he  were  to  give  a 
brief  account  of  the  steps,  taken  in  re- 
cent years,  to  solve  the  very  difficult 
question  of  the  economical  distribution 


115 

of  electricity  over  large  areas.  The 
paper  was,  as  the  author  had  himself 
said,  dry;  but  it  really  recounted  the 
gigantic  advances  that  had  been  made 
in  the  means  required  for  this  economical 
distribution  of  electricity.  It  was  only 
ten  years  since  Edison  solved  the  ques- 
tion of  incandescent  lamps,  and  only 
seven  years  ago  it  was  found  scarcely 
possible  to  distribute  currents  over  areas 
so  as  to  bring  electric  lighting  to  com- 
pare in  any  way  with  gas.  At  that 
time  a  distinguished  French  electrician, 
Mr.  Gaulard,  showed  how,  by  using  alter- 
nate currents  of  high  electromotive  force, 
to  distribute  electrical  energy  to  a  distance 
by  stepping  down,  as  it  were,  from  high 
pressure  to  low  pressure.  The  process 
was  similar  to  that  now  carried  out  in 
London,  to  distribute  power  by  means  of 
water  under  very  high  pressure  ;  also  to 
that  adopted  by  the  Gas  Light  and  Coke 
Company  at  Beckton,  to  send  gas  under 
high  pressure  to  holders  in  different 
parts  of  London,  and  there  distribute  it 
under  low  pressure.  Such  progress  had 


116 

been  made  in  America,  on  the  Continent, 
and  in  England,  that  ere  very  long  he 
believed  there  would  be  electric  lighting 
all  over  the  country.  There  was  hardly 
a  town  of  any  size  that  was  not  consider- 
ing the  subject,  and  that,  in  twelve 
months'  time,  would  not  be  on  the  road 
to  having  electric  lighting  distributed 
throughout  large  areas.  At  Deptford, 
there  was  the  extensive  enterprise  of  the 
London  Electrical  Supply  Corporation, 
and  the  enormous  machines  of  Ferranti 
were  being  constructed,  intended  to  pro- 
duce an  electric  pressure  equal  to  10,000 
volts,  representing  an  electromotive  force 
something  like  that  of  a  small  lightning 
flash.  It  would  be  driven  through  a 
very  small  conductor  up  to  the  neighbor- 
hood of  the  Monument,  and  would  there 
step  down  to  a  lower  pressure,  and  so  be 
distributed  throughout  the  city  of  Lon- 
don over  a  very  large  area.  One  was  the 
proper  rate  a"t  which  the  alternating  cur- 
rents should  be  transmitted.  The  prac- 
tice had  hitherto  been  to  commence  at  a 
very  high  rate.  Mr.  Ferranti  began  with 


117 

about  150  currents  (300  positive  and 
negative)  per  second,  but  by  practice  he 
had  come  down  to  the  figure  given  by 
the  author,  78.  He  had  omitted  to  men- 
tion that  throughout  Europe  the  alter- 
nate-current machines  were  being  con- 
structed principally  by  the  firm  of  Ganz, 
of  Budapest.  The  Zipernowsky  system 
had  been  introduced,  first  in  Italy,  and 
there  worked  out  thoroughly  by  a  dis- 
tinguished electrician,  Professor  Ferraris. 
In  the  Zipernowsky  system  the  frequency 
had  been  brought  down  from  150  cur- 
rents to  42.  Mr.  Parker  had  brought  it 
down  to  100.  That  was  one  of  the  most 
important  questions  to  be  decided,  and  it 
could  only  be  done  by  actual  practice. 
Sir  William  Thomson  had  shown,  by 
mathematical  reasoning,  that  if  currents 
were  sent  with  high  frequency,  they  had 
not  time  to  penetrate  into  the  interior  of 
a  conductor.  With  a  solid  conductor, 
say  between  Deptford  and  London,  one 
inch  thick,  at  a  high  frequency,  the  cur- 
rent would  not  enter  more  than  about  3 
millimeters  inside  the  surface ;  thus  the 


118 

only  part  of  the  copper  conductor  con- 
veying electricity  was  a  thin  shell  or  tube 
on  the  outside.  If  that  theory  was  true, 
the  lower  the  frequency,  the  greater 
the  efficiency  of  the  conductor.  Another 
reason  for  less  frequency  was  that  meters 
could  work  with  greater  accuracy. 

Professor  George  Forbes  congratula- 
ted the  author  on  the  many  points  of 
interest  he  had  brought  forward,  and 
especially  on  the  happy  way  in  which  he 
had  taken  in  hand  the  theoretical  inves- 
tigation of  alternate-current  machines. 
He  had  been  one  of  the  first  to  discuss 
the  theory  of  continuous-current  machines 
in  the  proper  fashion,  and  since  he  read 
his  paper  on  the  subject  before  the 
Institution  two  years  ago,  the  progress 
had  been  marked,  so  that  now  the  design 
of  continuous- current  machines  was  as 
straightforward  work  as  any  mechanical 
designs.  He  had  taken  up  the  subject  of 
alternate-current  machines  in  the  same 
spirit.  On  the  occasion  when  the  author 
read  a  paper  on  continuous -current 
machines.  Professor  Forbes  had  occasion 


119 

to  complain  of  the  combination  of  differ- 
ent kinds  of  units,  C.  G.  S.  and  English. 
He  was  sorry  to  find  the  same  practice  in 
the  present  paper,  and  he  wished  to 
enter  his  protest  against  it.  The  author 
spoke  of  the  mean  value  of  the  electro- 
motive force  of  an  alternating  current 
as  the  electromotive  force  of  a  direct 
current,  which  will,  in  a  given  re- 
sistance free  from  self-induction  (say, 
for  instance,  the  wire  of  a  Cardew 
voltmeter),  produce  the  same  amount  of 
heating.  That  was  not  a  definition  of 
the  mean  value  of  the  electromotive 
force  of  the  alternating  current.  He 
would  beg  the  author  to  withdraw  the 
expression  "  mean  value,"  and  substitute 
"  virtual  or  equivalent  value."  Until  a 
few  years  ago,  electricians  thought  that 
a  continuous  current  was  the  proper  one 
to  use  for  distribution,  and  that  the 
alternate  current  was  objectionable  for 
many  reasons.  But  now  they  were  quite 
agreed  that  the  alternate  current  was  in 
many  of  its  adaptations  far  more  beauti- 
ful and  more  readily  adapted  than  the 


120 

continuous  current.  It  was  due  to 
Messrs.  Gaulard  and  Gibbs  that  a  system 
of  transformation  from  high  to  low  pres- 
sure was  economical,  and  could  be 
adopted  in  central-station  distribution. 
If  any  one  doubted  the  value  of  the  work 
done  by  those  gentlemen,  he  would  ask 
what  would  be  the  present  position  of 
electric  lighting  if  Messrs.  Gaulard  and 
Gibbs  had  not,  during  two  or  three  years 
of  persistent  opposition  on  the  part  of 
electrical  engineers,  forced  upon  electri- 
cians the  conclusion  that  the  use  of  their 
secondary  generators  was  an  economical 
mode  of  distributing  electricity?  While 
great  credit  was  due  to  the  author  for 
having  introduced  his  theoretical  views 
on  the  question  of  alternators,  it  was 
unfortunate  that  he  had  not  given  more 
numerical  facts  as  to  alternating 
dynamos,  as  to  the  efficiency  of  the 
transformers,  and  so.  on.  Such  data 
were  very  desirable.  The  author  had 
raised  the  question  whether  dynamos 
ought  to  be  worked  in  parallel  or 
separately.  On  the  ordinary  contin- 


121 

uous  system,  as  first  generally  adopted 
by  Edison  and  now  universally  employed, 
it  was  customary  to  have  all  the  mains  in 
the  district  connected  together  into  a 
large  network,  with  feeding  cables  going 
to  different  points.  Those  feeders,  all 
issuing  from  the  central  station,  were 
connected  to  one  set  of  mains,  and  all  the 
dynamos  were  connected  in  parallel  to 
those  mains,  all  working  together.  There 
was  a  difficulty  in  alternate  currents  work- 
ing in  parallel,  and  it  was  customary 
not  to  make  a  single  network  over  the 
whole  of  a  district,  but  to  subdivide  it 
into  small  districts,  each  with  its  separate 
feeder,  and  each  feeder  might  be  fed  by 
a  separate  machine  or  a  number  of  the 
feeders  might  be  grouped  on  to  one 
machine.  At  the  beginning  of  the 
evening's  work  all  the  feeders  would  be 
upon  one  machine.  As  the  consumption 
of  electricity  increased,  some  of  the 
feeders  would  be  passed  on  to  another 
machine,  and  so  on.  The  author  con- 
sidered it  impossible  to  switch  the  feeders 
on  to  a  new  dynamo  without  making 


122 

some  flickering  in  the  light.  In  the 
course  of  last  year  Professor  Forbes  had 
examined  a  very  large  number  of  central 
stations,  and  the  alleged  difficulty  did 
not  exist.  The  facility  of  switching  in 
dynamos  without  producing  a  flicker 
depended  simply  on  the  kind  of  switch 
employed.  With  a  rapid  switch  there 
was  no  difficulty.  He  had  lately  examined 
the  central  station  at  Borne,  set  up  by 
Messrs.  Ganzand  Company,  and  there  was 
there  a  switch-board  of  very  great 
ingenuity,  designed  by  Mr.  Blathy.  As 
to  the  possibility  of  working  conveniently 
in  parallel  he  might  say  that  experience 
in  America  had  been  completely  against 
it.  It  was  there  found  that  it  was  possi- 
ble to  work  in  parallel,  but  that  it 
enormously  increased  the  amount  of 
skilled  attention  required  in  a  central 
station ;  and  for  that  and  other  reasons 
it  was  far  better  to  divide  the  district 
into  a  number  of  sub-districts,  feeding  by 
separate  feeders  from  the  station.  That 
method  had  also  another  advantage, 
especially  in  a  country  like  America, 


123 

where  overhead  wires  were  chiefly  em- 
ployed. There  was  another  reason  why 
in  America  it  had  been  preferred  not  to 
work  in  parallel,  and  that  was  that  the 
alternations  of  current  in  the  machines 
were  more  frequent,  and  such  machines 
could  not  be  worked  in  parallel  so  easily 
as  those  which  had  a  small  number 
of  alternations.  Dynamo  machines  for 
alternate  currents  might  be  divided  into 
two  classes,  those  which  had  little  or  no 
self-induction,  and  those  which  had  large 
self-induction.  The  Siemens  machine 
was  one  of  those  with  little  or  no  self- 
induction,  and  the  Mordey  machine  was 
another  of  the  same  type.  The  armature 
of  the  Mordey  machine  looked  very  like 
that  of  the  Siemens  machine ;  but  it  was 
a  fixture,  and  the  Mordey  machine  had  a 
peculiarity,  in  common  with  the  Kennedy 
machine,  which  made  it  extremely  origi- 
nal. In  machines  of  the  Siemens  and 
Mordey  types,  where  there  was  no  self- 
induction,  if  it  was  desired  to  introduce 
it,  all  that  had  to  be  done  was  to  put 
large  self-induction  into  the  circuit.  This 


124 

was  as  convenient  as  to  put  the  self-in- 
duction into  the  machine  itself.  Still, 
there  was  a  good  deal  to  be  said  in  favor 
of  machines  of  iron.  One  advantage  was 
that  the  clearance  between  the  poles  and 
the  armature  was  smaller,  and  there- 
Figs.  27 


SINGLE-COIL  ALTERNATOR. 
Scale  TV . 

fore  the  magnetization  could  be  got  at  a 
cheaper  rate.  One  of  the  great  advances 
in  alternators  of  ]ate  years  was  the  in- 
vention of  the  Mordey  machine.  *  Up  to 
that  time  alternate- current  machines  were 


125 

made  with  a  large  number  of  pole-pieces. 
The  Mordey  machine  had  two ;  in  the 
old  type  each  pole-piece  had  its  magnet- 
izing coil,  and  there  was  great  waste  of 
energy.  Mr.  Mordey  had  introduced 
the  idea  of  using  a  single  coil  to  magnet- 
ize the  whole  machine.  Professor  Forbes 
had  been  experimenting  a  little  in  that 
direction,  and  had  thought  it  might  be 
worth  while  to  exhibit  a  rough  diagram 
of  a  design,  of  a  somewhat  similar  kind, 
in  which  not  only  was  a  single  coil  used 
for  the  magnetizing  circuit,  but  a  single 
coil  was  also  used  for  the  induced  circuit 
(Figs.  27).  The  induction  through  the 
radial  parts  of  the  field  magnet  was  con- 
stant. To  prevent  heating,  it  might  be 
necessary  to  subdivide  the  iron  at  the 
pole-pieces  into  circular  sheets ;  but  that 
would  be  seen  when  the  first  machine 
was  made.  That  type  of  machine  was 
certainly  of  interest,  and  might  prove  of 
value.  The  Parsons  machine  seemed  to 
him  to  fulfill  the  requirements  of  an 
alternator  better  almost  than  anything 
else  which  had  been  produced.  It  also 


126 

had  the  advantage  of  having  a  single 
current  for  the  field  magnet,  and  a  single 
current  for  the  induced  armature.  He 
would  only  say  a  word  on  the  subject  of 
the  speed  of  alternations.  Why  was  it 
that  in  America  16,000  alternations  per 
minute  were  used,  and  in  Europe  at  the 
greatest  number  of  stations  5,000 1  One 
reason  was,  that  in  America  high-speed 
machines  were  in  favor,  and  in  Europe 
low  speed.  Another  reason  was  that,  in 
America,  the  object  aimed  at  was  to  get 
the  greatest  output  from  the  plant. 
Those  reasons  were  sufficient  for  having 
high-speed  alternations.  Unless  it  was 
wished  to  work  in  parallel,  it  could  not 
be  doubted  that  working  with  the  high- 
est-speed alternations  was  best ;  but  for 
working  in  parallel  there  could  be  no 
doubt  that  the  lowest  speed  was  the 
most  easy  mode.  That  was  one  reason 
why  the  Ganz  machines  at  Rome  were  so 
suitable.  In  this  country  there  was  a 
general  belief  that  converters  had  an 
efficiency  of  95  or  96  per  cent,  on  full 
load ;  but  the  greater  number  of  con- 


127 

verters  used  in  England  had  nothing  like 
that  efficiency.  The  smaller  converters 
used  by  Messrs.  Ganz  and  Co.  certainly 
had  nothing  like  it ;  they  guaranteed  an 
efficiency  of  88  per  cent.  The  machines 
exhibited,  the  Lowrie  converter,  the 

Fig.  28 


CURRENT  OUTPUT.    GROSVENOR  GALLERY. 

Kapp  converter,  and  still  more  the  Fer- 
ranti,  had  all  a  high  magnetic  resistance, 
which  he  was  inclined  to  think  would  be 
unfavorable.  He  knew  that  tests  had 
been  made  with  a  Kapp  converter  by 
Professor  Ayrton,  but  in  totally  differ- 


128 

ent  conditions  from  the  machines  shown, 
and  he  should  be  surprised  if  they  had 
the  same  efficiency  as  that  shown  by 
Professor  Ayr  ton.  He  might  take  one 
example,  which  was  very  prominent, 
namely,  the  converters  used  by  the  Gros- 
venor  Gallery.  The  diagram  (Fig.  28) 
showed  the  output  of  amperes  in  a  day, 
and  it  would  be  seen  that  between  four 
and  seven  hours  in  the  morning,  when 
no  lamps  were  on  circuit,  there  was  an 
indication  of  four  thousand  lamps  being 
on  circuit  according  to  the  ampere- 
meters of  the  central  station ;  that  meant 
a  waste  of  nearly  four  thousand  lamps 
always  going  on,  and  with  higher  loads 
the  loss  was  greater.  The  loss  as  shown 
in  the  diagram  was  20  per  cent,  of  the 
maximum  with  no  load ;  consequently 
when  there  was  any  load  on,  the  efficiency 
was  certainly  not  80  per  cent. 

Mr.  Llewelyn  Atkinson  said  that  the 
constants  which  the  author  had  de- 
veloped, and  which  were  very  useful  in 
comparing  the  electromotive  force  of 
alternating  machines  with  machines  of  a 


129 

continuous  type,  seemed  to  him  might  be 
made  more  useful  if  they  were  more 
separated.  The  constant  K  appeared  to 
contain  three  things.  First,  it  contained 
a  multiplier  of  2,  introduced  because 
alternate-current  machines  generally  had 
only  a  single  circuit,  not  two  circuits,  but 
this  was  not  always  the  case,  and  the 
multiplier  2  should  be  put  separately. 
Secondly,  the  constant  included  a  quan- 
tity depending  on  the  shape  of  the  field 
and  the  arrangement  of  the  armature; 
and  thirdly,  the  quantity  depending  on 
the  ratio  of  the  square  root  of  the  mean 
square  to  the  mean.  All  those  three 
quantities  appeared  to  be  mixed  up  in 
one  number,  which  might  be  useful  in 
the  particular  cases  given,  but  he  thought 
that  if  they  were  dealt  with  as  he  sug- 
gested they  would  be  more  useful  to 
subsequent  designers.  Nearly  all  cases 
which  the  author  had  treated  so  lucidly 
as  to  connecting  machines  in  parallel, 
had  been  by  the  graphic  method,  which 
depended  entirely  upon  the  assumption 
that  the  electromotive  force  followed  a 


130 

law  of  simple  harmonic  motion.  He  was 
aware  that  there  were  great  difficulties  in 
treating  it  in  any  other  way.  First  of  all 
the  law  itself  had  to  be  found ;  and 
secondly,  he  did  not  know  of  any  graphic 
method  of  solving  the  problems  when 
the  law  had  been  found.  The  analytical 
method  was  probably  even  more  difficult. 
It  was  generally  complicated  enough 
even  with  a  simple  harmonic  law,  but 
with  irregular  laws  he  did  not  know  that 
it  could  be  touched  at  all.  He  had 
therefore  brought  a  diagram  showing 
what  were  likely  to  be  the  errors  even  in 
the  machines  the  author  had  treated  of, 
taking  the  harmonic  law  to  be  true.  In 
Figs.  29,  the  curves  1,  2,  and  3  showed 
the  primary  electromotive  force  induced 
in  a  coil  all  wound  in  a  single  line  on  the 
armature,  by  moving  it  through  three 
different  forms  of  magnetic  field,  a  har- 
monic field,  a  field  such  as  occurred  in 
the  Mordey  machines,  and  a  field  such^as 
was  given  by  the  author's  machine  with 
opposite  poles  alternately  on  each  side 
of  the  ring,  with  a  space  equal  to  the 


131 

width  of  pole.  1.  Gave  a  curve  of 
primary  current  in  a  circuit  with  self- 
induction  which  was  also'harmonic,  and 
a  curve  of  secondary  electromotive  force 
also  harmonic.  2.  Gave  a  curve  of  pri- 
mary current  similar  in  form  to  the 

Figs.  29 


Primary 


curve  of  electromotive  force,  but  with  all 
the  corners  rounded  and  the  rises  and 
falls  less  abrupt ;  but  the  curve  of 
secondary  electromotive  force  was  differ- 
ent, and  showed  rapid  rises  and  falls 
and  intervals  of  no  electromotive  force. 


132 

3.  Gave  the  same  class  of  results  as  re- 
garded primary  electromotive  force  and 
current ;  but  here  also  the  curve  of 
secondary  electromotive  force  was  very 
different.  Owing  to  the  fall  in  positive 
value  of  electromotive  force  being  dis- 
continuous with  the  rise  in  negative 
electromotive  force,  there  were  two  im- 
pulses of  secondary  electromotive  force, 
corresponding  to  each  impulse  of  primary 
electromotive  force.  The  effect  of  this 
was  to  double  the  loss  from  magnetic 
friction,  or  hysteresis,  in  any  magnetic 
apparatus  in  the  secondary  circuit.  That 
at  once  showed  the  very  important  bear- 
ing of  the  question  of  the  law  of  elec- 
tromotive force,  and  the  errors  that 
might  be  introduced  by  assuming  a 
simple  sine-function.  He  had  alluded  to 
the  difficulty  of  treating  the  matter  ana- 
lytically and  graphically ;  but  there  was 
one  mode  of  treating  it  which  he  had  not 
seen  mentioned,  the  idea  of  which  oc- 
curred to  him  two  years  ago,  and  he  had 
designed  some  machines  for  carrying  it 
out,  namely,  treating  the  subject  by  means 


133 


of  the  integrator  (Figs.  30).  To  take  the 
simplest  case  of  a  circuit,  of  which  the 
induction  and  resistance  were  known,  and 

\ 


\ 


\ 


the  law  of  electromotive  force  was  given 
by  means  of  a  curve.  Let  a  b  c  d  be  an 
integraph  in  skeleton  consisting  of  a  rect- 


134 

angular  frame.  In  this  frame  slid  a 
cross-bar  e'  /,  and  within  an  inner  slide 
a  b  g  A,  a  carrier  through  which  was 
pivoted,  on  a  vertical  axis,  an  integrating 
roller.  The  angular  position  of  this  roll- 
er was  fixed  by  a  rod  k  e,  sliding  at  e 
through  a  pivot  6,  free  to  move  round  in 
a  horizontal  plane.  The  whole  frame 
could  only  move  in  a  direction  parallel  to 
the  axis  of  x,  being  constrained  by  guides 
or  rollers.  Through  the  bar  e'  f  at  m 
passed  a  pointer.  Let  xt  yt  be  co-ordi- 
nates of  a  point  on  the  curve  of  primary 
electromotive  force,  let  x  y  be  co-ordi- 
nates of  the  curve  traced  by  the  non- 
slipping  integrator  roller.  Then  by  the 
construction  of  the  apparatus  the  follow- 
ing relations  held  good.  The  roller  was 
always  tangential  to  the  curve  x  y,  and 


d  x  me 

Let   the   scale  of  y   be   such   that  y 

Tjl  T 

=  •  _,  and  let  m  e  =  _,  where  L  and  K 

II  B 

were   coefficients  of    self-induction    and 
resistance. 


135 

-  -y 

Then  ^  =  ? -,  and  if  the  co-ordi- 

dx          L 

5 

nates  x  y  represented  current  and  time 

--C 

respectively,  —  =  5 ,  or  L  —  4-   C 

at          L  d  t 

II 

E  =  E,  the  well-known  equation  of  a 
single  electric  circuit.  Thus,  by  means 
of  the  integrator,  any  curve  of  electro- 
motive force  being  given,  it  was  possible 
to  draw  the  curve  of  the  current.  He 
had  further  designed  machines  which  it 
would  take  too  long  to  describe,  in  which 
with  two  circuits,  given  the  coefficients 
of  self-induction,  the  coefficient  of  mutual 
induction,  and  the  resistances,  with  a 
given  curve  representing  the  primary 
electromotive  force,  the  curve  of  primary 
current,  the  curve  of  secondary  electro- 
motive force,  and  the  curve  of  secondary 
current  could  be  deduced ;  and  all  the 
curves,  their  shapes,  their  retardation, 
and  everything  about  them. 


136 

Mr.  James  Swinburne  considered  that 
the  author's  papers  gave  rise  to  very 
good  discussions,  partly  because  they 
were  of  great  value,  partly  because  he 
always  selected  a  subject  which  was 
fashionable  at  the  moment,  and  partly 
because  he  always  gave  a  good  deal  to 
disagree  with.  With  regard  to  the 
author's  assumption  of  the  curve  of  sinesr 
he  could  not  see  how  that  afforded  any 
help.  In  practical  work,  the  only  use  he 
had  ever  found  in  the  curve  of  sines  was 
in  seeing  whether  an  instrument,  which 
had  really  a  coefficient  of  self-inductionr 
would  give  a  reading  within  a  certain 
percentage  error.  But  in  dealing  with 
machines  the  assumption  seemed  to  him 
to  be  an  absurdity.  It  was  only  taken 
because  it  admitted  of  a  great  many 
mathematical  calculations;  but  if  the 
mathematical  calculations  were  based 
upon  empirical  data  he  thought  it  was  a 
pity  to  make  them.  Of  course  it  was 
continually  said  that  by  Fourier's  theo- 
rem any  curve  could  be  made  up  of 
curves  of  sines.  In  practical  work  elec- 


137 

tricians  never  dealt  with  anything  that 
had  constant  coefficients  of  self-induction 
or  mutual  induction,  except  measuring 
instruments ;  and  in  dealing  with  trans- 
formers, incandescent  lamps,  and  so  on, 
nothing  of  the  sort  came  in.  He  thought 
that  all  the  comparisons  in  the  paper 
between  direct  and  alternate-current 
machines  were  based  on  an  assumption 
which  made  them  misleading.  The 
assumption  was  that  the  direct  machines 
had  the  same  number  of  armature  turns 
as  the  corresponding  alternate  machines. 
In  practice  he  did  not  think  that  any- 
body ever  made  the  air-gap  otherwise 
than  equal  to  the  breadth  of  the  pole. 
The  output  varied  as  the  product  of  the 
number  of  useful  wires  in  a  coil,  and  the 
breadth  of  the  pole-piece.  The  product 
was  greatest  when  they  were  equal,  and, 
consequently,  designers  always  made 
them  equal.  The  fringe  of  useful  field  at 
the  edge  of  the  pole-pieces  must  be 
allowed  for ;  and  in  some  cases  the  ques- 
tion was  complicated  by  the  sides  of  the 
coils  being  parallel,  and  the  sides  of  the 


138 

pole-pieces  radial,  as  in  the  author's 
machine.  The  author  assumed  a  con- 
stant coefficient  of  self-induction  in  the 
armature.  In  the  machine  which  had 
originated  the  unwarrantable  assumption 
of  the  curve  of  sines  the  self  -  induction 
was  nearly  constant.  It  was  a  Siemens 
machine  used  by  Mr.  Joubert.  There 
was  very  little  iron  near  the  armature, 
and  the  coefficient  of  self-induction  was 
sensibly  constant.  In  the  modern  ma- 
chine there  was  not  a  constant  coefficient 
of  self  induction  in  the  armature.  This 
would,  he  was  afraid,  detract  from  the 
usefulness  of  Mr.  Atkinson's  ingenious 
application  of  the  integraph.  The  sim- 
plest way  of  calculating  these  things  was 
not  to  take  the  coefficients  of  self-induc- 
tion, but  to  find  out  how  many  lines  of 
force  were  cutting  the  circuit  at  any 
time,  by  plotting  the  field-magnets  out, 
and  working  through  a  graphic  method. 
It  was  a  long  and  tedious  process,  but  it 
could  be  done,  and  done  with  the  same 
accuracy  as,  for  example,  Professor 
Forbes'  dynamo  leakage  calculations.  In 


139 

the  direct-current  dynamo  the  term  self- 
induction  had  been  a  sort  of  scapegoat 
for  all  sorts  of  vague  notions.  Even 
now,  in  the  case  of  direct-current  ma- 
chines, people  talked  about  the  self- 
induction  of  the  armature.  Of  course 
there  was  no  such  thing  in  direct-current 
machines,  and  the  idea  was  an  absurdity. 
In  alternating  currents,  the  same  accusa- 
tion could  not  be  brought,  as  the  whole 
armature  current  varied.  With  regard 
to  motors,  he  thought  the  author's  ideas 
were  a  little  elementary  for  the  present 
day.  With  a  big  motor,  running  at  dif- 
ferent loads,  it  was  found  that  the 
efficiency  was  extremely  small  if  depend- 
ence was  placed  simply  on  self-induction 
to  keep  the  motor  and  dynamo  in  step. 
He  did  not  think  that  motors  which  de- 
pended on  self-induction  for  keeping  in 
step  would  answer.  Many  seemed  to 
think  the  chief  difficulty  was  to  start  the 
motor.  This  was  really  a  small  matter. 
All  that  had  to  be  done  was  to  make  a 
self -exciting  motor.  Take  the  commuta- 
tor machine  made  by  the  Thomson- 


140 

Houston  Company,  and  put  it  on  an 
alternate-current  circuit,  it  would  start, 
sparking  badly  at  first,  and  eventually 
synchronize.  There  was  no  difficulty  in 
starting  the  motor,  but  it  would  not 
work  efficiently.  The  author  had  asked 
how  it  was  that  the  waste  power  was 
greater  in  the  armature  conductors  of  a 
machine  without  iron  in  the  armature. 
It  was  because  the  change  of  field  was 
more  abrupt  in  that  case.  A  great  deal 
had  been  said  at  different  times  about 
the  advantage  or  disadvantage  of  iron  in 
the  armature,  and  it  had  been  discussed 
both  from  a  mechanic's  and  from  an 
electrician's  point  of  view ;  but  when  it 
was  remembered  that  the  air-space  (in 
spite  of  what  Professor  Forbes  had 
stated)  was  really  the  same  whether  there 
was  iron  in  the  armature  or  not,  it  would 
be  seen  that  the  whole  question  was  one 
of  mechanical  construction  against  elec- 
trical efficiency.  If  there  was  iron,  power 
would  be  lost  in  the  reversal  of  mag- 
netization. If  there  was  none,  there 
must  be,  to  a  certain  extent,  flimsiness. 


141 

There  might  be  a  more  efficient  machine, 
but  there  was  mechanical  flimsiness.  A 
great  deal  had  been  said  about  hysteresis. 
He  considered  the  author's  inductions 
from  Professor  Swing's  paper  were  faulty. 
Plotting  out  the  curve  from  that  paper, 
or  from  Dr.  Hopkinson's  paper,  it  would 
be  found  that  up  to  an  induction  of 
about  1(>,000,  the  power  spent  with  a 
given  alternation  frequency  varied  sensi- 
bly as  the  induction.  The  author's 
argument,  that  if  there  was  half  the 
induction  there  was  half  the  heat  per 
cubic  centimeter,  was  all  very  well,  but 
then  twice  the  iron  must  be  used  to  get 
the  same  output.  And  it  was  found  that 
in  transformers  made  according  to  pres- 
ent practice  with  low  inductions,  in  which 
most  of  the  heat  was  wasted  in  the  iron, 
as  it  was  in  transformers  of  any  reason- 
able size,  the  speed  of  alternation  made 
very  little  difference  theoretically  in  the 
output.  He  said  theoretically,  because 
not  enough  was  known  about  the  time 
lag,  and  if  that  was  great,  larger  outputs 
could  be  obtained  with  few  alternations. 


142 

He  was  aware  that  he  was  disagreeing 
with  Professor  Forbes  on  that  point.  He 
hoped  Mr.  Atkinson  would  be  able  to 
supply  some  particulars  as  to  time  lag, 
that  he  would  run  the  machine  at  differ- 
ent speeds  and  give  the  results.  The 
kind  of  time  lag  mentioned  by  Professor 
Ewing  was  well  known  to  dynamo 
makers,  and  the  phenomenon  was  fa- 
miliarly known  as  "  creeping  up."  A 
new  machine  sometimes  took  twenty 
minutes  to  reach  its  full  excitation. 
Messrs.  Crompton  &  Company  were 
making  experiments  on  the  important 
question  of  loss  of  power  in  iron  in 
alternate-current  work,  which  he  hoped 
would  be  published.  The  question  of 
hysteresis  concerned  transformers  as  well 
as  dynamos.  He  thought  that  most 
people  used  bad  iron.  In  testing  iron 
for  direct-current  machines  they  only 
thought  whether,  with  a  given  excitation, 
they  could  get  iron  highly  magnetized. 
That  was  not  the  important  question  in 
alternating  currents.  The  question  of 
hysteresis  must  be  considered.  There 


143 

was  a  great  difference  in  samples  in  that 
respect.  He  had  made  transformers 
which  would  work  with  very  high  induc- 
tion without  heating.  One  of  the  most 
important  questions  to  settle  was  fre- 
quency of  alternation.  It  had  been  stated 
that  in  America  16,000  alternations  per 
minute  had  been  taken,  and  at  Home 
5,000,  and  what  should  be  made  the 
standard  in  England  should  be  carefully 
considered.  In  dynamo  construction  he 
found  that  it  was  easier  to  make  a  ma- 
chine giving  a  very  few  alternations.  In 
that  way  he  could  construct  a  larger 
dynamo  for  the  same  amount  of  money, 
and  make  it  work  more  efficiently.  The 
first  point  to  be  settled  was  the  number 
of  vibrations  per  second  which  could  be 
separated  by  the  eye.  Helmholtz,  in  his 
"  Sensations  of  Tone  as  a  basis  for  the 
Theory  of  Music,"  gave  24  per  second. 
Messrs.  Crompton  were  going  to  try 
some  experiments  to  ascertain  whether  it 
was  possible  to  detect  flickering  in  100- 
volt  lamps  with  anything  below  24  vibra- 
tions per  second.  It  was  a  pity  that  the 


144 

author  had  not  been  able  to  say  some- 
thing about  the  Tesla  motor.  The  first 
form  was  hardly  a  practical  alternating 
motor,  because  it  required  three  leads ; 
and  if  a  third  lead  was  run,  a  direct  cur- 
rent might  as  well  be  used,  with  motors 
which  it  was  known  could  work  efficiently. 
But  he  thought  that  he  had  heard  some- 
thing about  a  lagging  transformer,  and 
he  should  like  to  know  more.  The 
author  had  called  the  Mordey  alternator 
an  iron-clad  machine.  He  considered 
the  word  iron-clad  a  bad  one  to  use.  It 
was  employed  some  time  ago  to  denote  a 
machine  in  which  the  iron  was  wrapped 
round  the  copper ;  the  idea  was  that  a 
line  integral  of  the  magnetic  force  of 
more  than  0.4  n  time  the  ampere  turns 
could  somehow  be  obtained ;  but  that 
fallacy  had  been  dropped,  and  it  was  a 
pity  to  use  the  word  for  the  Mordey 
machine,  where  the  only  object  was  to 
get  the  whole  field  through  one  exciting 
coil.  The  fault  of  the  Kennedy  machine, 
as  far  as  it  had  any,  was  the  want  of  ven- 
tilation. One  of  the  great  beauties  of  the 


145 

Mordey  machine  was  that  it  could  be  run 
with  a  high-current  density  without  fear. 
It  had  occurred  to  him  that  if  an  iron 
core  were  put  into  the  Mordey  machine, 
and  the  field-poles  were  arranged  to 
come  alternately,  as  in  the  Kennedy 
machine,  instead  of  opposite,  the  power 
of  the  machine  would  be  doubled  without 
greatly  increasing  the  expense.  He 
agreed  with  Professor  Forbes  as  to  the 
credit  due  to  Messrs.  Gaulard  and  Gibbs, 
which,  he  thought,  ought  to  be  frankly 
acknowledged. 

The  Hon.  Charles  Parsons  said,  as  the 
calculations  in.  the  paper  were  based  on 
the  sine-function,  he  would  refer  to  a  few 
figures  in  connection  with  a  bipolar 
alternator,  in  which  the  sine-function  was 
nearly  realized.  With  two  poles,  and 
one  continuous  coil,  or  two  half-coils,  as 
on  the  drum  of  the  armature,  Fig.  8,  the 
electromotive  force  was  a  sine-function, 
and  the  self-induction  was  considerable. 
In  a  contemplated  machine,  the  output 
of  which  was  intendedtto  be  75,000  watts, 
the  current  to  excite  the  magnets  would 


146 

be  about  1  per  cent,  of  the  output,  and 
the  loss  in  resistance  of  the  armature 
about  1^  per  cent.  This  machine  (Fig. 
31)  was  not  yet  completed,  but  one  of  30 
units  had  been  made  and  carefully  tested. 
With  regard  to  the  question  of  hysteresis, 
he  had  made  experiments  upon  the  loss 
in  the  armature.  A  cylindrical  armature - 
core,  5  inches  in  diameter,  composed  of 
one  hundred  iron  plates  to  the  circle, 
insulated  from  each  other  by  thin  paper, 
but  not  insulated  from  the  spindle,  was 
rotated  in  a  bi-polar  field.  The  energy 
required  to  rotate  the  core  when  sub- 
jected to  different  intensities  of  field,  and 
at  different  speeds  of  rotation,  was  meas- 
ured by  independent  means.  In  one 
experiment  the  same  core  was  rotated, 
first  at  8,500  revolutions  per  minute,  and, 
secondly,  at  6,500,  the  strengths  of  field 
being  maintained  in  the  two  cases  in- 
versely proportional  to  the  speeds  ;  or, 
in  other  words,  the  electromotive  force, 
had  the  core  been  wound  with  conduct- 
ing wire,  would  have  been  identical  in  the 
two  cases.  It  was  found  that  the  power 


147 

lost  by  hysteresis  at  the  lower  speed  was 
approximately  25  per  cent,  greater  than 
at  the  higher  speed.  Taking  the  energy 
absorbed  per  revolution  in  the  two  cases, 
it  followed  that  the  loss  per  reversal  was 
approximately  proportional  to  the  square 
of  intensity  of  field.  Some  other  ex- 
periments had  been  made  which  went  to 
show  that  the  viscous  hysteresis,  or  the 
viscous  resistance  of  the  iron  to  rapid 

Fig,  31 


TURBO  ELECTRIC-GENERATOR  FOR  75,000  WATTS 
FOR  ALTERNATING  CURRENTS. 

change  of  polarity,  was  a  comparatively 
small  quantity.  The  intensity  of  field  in 
the  above  experiments  was  between  5,000 
and  7,000.  At  6,000  revolutions  of  the 
apparatus  the  loss  would  be  2  HP.,  which 
was  about  2  per  cent,  of  the  output,  mak- 
ing a  total  electric  efficiency  of  9->  or  96 
per  cent,  for  the  dynamo.  The  machine 


148 

was  arranged  with  an  electric- control 
governor,  which  was  compounded  so  as  to 
keep  the  electromotive  force  at  the 
terminals  constant  at  all  loads.  Though 
the  machine  revolved  at  a  high  rate  of 
speed,  the  wear  and  tear  was  exceedingly 
small,  the  same  bearings  having  been 
running  for  three  years  without  any  per- 
ceptible wear. 

Mr.  W.  B.  Esson  observed  that  most 
of  the  points  he  might  have  referred  to 
had  been  taken  up  by  other  speakers. 
The  induction-curve  in  the  Mordey  alter- 
nator would  differ  considerably  from  the 
curves  shown  by  Mr.  Atkinson,  for  two 
or  three  reasons.  The  first  was  that  the 
coil  in  the  alternator  was  not  merely  a 
rectangle  concentrated  in  one  wire,  as 
would  be  required  to  give  the  particular 
curve  in  2,  but  a  number  of  wires  occupy- 
ing a  considerable  angular  width.  An- 
other reason  was  that,  owing  to  the 
trapezoidal  form  of  coil,  the  induction 
commenced  very  gradually,  and  rounded 
off  the  corners  in  the  diagram.  The 
peculiarity  of  that  alternator  was  that  the 


149 

induction-curve  of  individual  coils  was  not 
symmetrical,  but  as,  in  the  machine,  the 
coils  were  joined  in  pairs,  it  came  out  that, 
though  considering  any  coil  by  itself  there 
was  a  want  of  symmetry,  when  the  coils 
were  joined  up  all  in  series,  the  induction- 
curve  of  the  whole  machine  was  quite 
symmetrical ;  it  was  almost  exactly  a 
curve  of  sines.  Mr.  Mordey  had  meas- 
ured the  induction  through  a  pair  of  coils 
for  all  different  positions  of  the  field- 
magnet  in  a  whole  period,  and,  as  the 
curves  showed  that  the  induction  lay 
within  the  curves  of  sines  at  some  parts, 
so  the  curve  for  the  electromotive  force 
lay  at  some  parts  outside  the  curve  of 
sines.  He  should  like  to  have  some 
definite  information  regarding  the  amount 
of  power  required  to  reverse  the  mag- 
netism in  the  ring- cores  of  alternating 
dynamos  for  different  degrees  of  mag- 
netization. He  had  been  making  some 
investigations  into  the  subject,  and  had 
found  that  to  prevent  the  cores  of  alter- 
nate-current dynamos  from  over- heating, 
the  thickness  of  the  iron  core  for  100 


150 

periods  per  second  should  not  exceed  9 
centimeters,  with  a  saturation  of  7,000 
C.G.S.  units. 

Mr.  A.  A.  Campbell  Swinton  said  there 
seemed  to  be  an  impression  amongst 
engineers  generally,  that  very  high-speed 
machines  like  the  Parsons  must  sacrifice 
durability.  At  Sir  William  Armstrong's 
works  at  Newcastle  there  were  three 
Parsons  machines,  two  of  which  ran  at 
about  9,000  revolutions  per  minute,  and 
the  other  at  about  17,000.  They  had 
been  running  for  three  years,  and  neither 
the  bearings  nor  the  spindles  had 
appreciably  worn  away.  He  thought 
that  the  brushes  and  the  commutators 
were  the  only  parts  which  had  been  re- 
newed. Of  course  the  Parsons  machine 
was  a  special  machine,  and  the  bearings 
were  specially  designed  to  suit  the  high 
speed.  The  fact  that  high  speed,  had 
not  received  much  attention  was  not  the 
fault  of  electricians,  but  of  engineers.  If 
engineers  had  produced  engines  that 
would  run  at  these  high  speeds,  no 
doubt  electricians  would  have  produced 
dynamos  for  them. 


151 

Mr.  F.  H.  Nalder  observed  that  the 
insulation  resistance  between  the  primary 
and  secondary  coils  was  important  in  the 
transformer.  It  was  also  of  very  great 
moment  to  apparatus  in  houses,  which,  if 
the  insulation  should  break  down,  would 
be  liable  to  cause  fire.  That  in  a  meas- 
ure was  looked  after  by  most  makers, 
who  provided  covers  for  the  transformers. 
Engineers  should  come  to  the  same  con- 
clusion with  respect  to  the  minimum  insu- 
lation resistance  between  primary  and 
secondary  coils,  and  also  between  the 
primary  coils  and  the  frame. 

Professor  W.  E.  Ayrton  remarked  that 
although  some  points  in  the  paper  might 
be  not  quite  right,  it  was  of  a  highly 
suggestive  character.  He  wished  to 
follow  those  who  had  preceded  him  in 
condemning  the  expression  "mean  elec- 
tromotive force  "  employed  in  the  paper. 
The  expression  had  now  a  perfectly 
definite  signification  in  connection  with 
alternate-current  circuits ;  it  was,  there- 
fore,  a  mistake  to  use  it  as  a  substitute 
for  another  expression  which  had  also  a 


152 

clear  significance — "the  square  root  of 
the  mean  square."  The  two  things  differ 
by  many  per  cent.,  depending  on  what 
function  the  electromotive  force  was  of 
the  time.  The  mean  electromotive  force 
of  an  alternate-current  and  a  direct-cur- 
rent dynamo  similarly  constructed,  must 
be  identical.  Whether  the  wire  was  piled 
up  all  at  one  place,  or  whether  spread 
uniformly  round  the  armature,  as  in  a 
direct- current  dynamo,  the  mean  electro- 
motive force  must  necessarily  be  the 
same.  The  author  spoke  of  "  English 
lines  of  force."  There  was  no  such  thing 
as  an  English  line  of  force  ;  lines  of  force 
were  essentially  cosmopolitan.  One  of 
the  great  charms  that  the  absolute 
system  of  electrical  and  magnetic  units 
possessed  was  its  perfect  harmony,  and 
therefore  any  attempt  to  introduce  new 
units  should  be  deprecated.  Experi- 
ments made  at  the  Central  Institution, 
for  finding  the  coefficient  of  self-induc- 
tion of  a  transformer,  showed  that  in  no 
case  was  there  no  lag  between  the  im- 
pressed electromotive  force  and  the  pri- 


153 

mary  current.  Measurements  had  also 
been  made  by  a  number  of  students  to 
ascertain  the  lag  between  the  primary 
and  the  secondary  current.  The  second- 
ary circuit  was  sending  a  current  through 
a  non-inductive  resistance.  For  all 
speeds  varying  from  about  1,600  semi- 
alternations,  up  to  16,000  semi-alterna- 
tions per  minute,  there  appeared  to  be  a 
lag  of  about  90°  above  the  lag  which 
ought  to  be  got,  which  would  really  cor- 
respond to  the  maximum  lag  possible. 
In  fact,  there  seemed  to  be  a  considerable 
amount  of  self-induction  in  a  transformer, 
even  when  the  secondary  circuit  was 
employed  to  send  a  current  through 
glow-lamps,  or  a  non-inductive  circuit. 
Without  lag,  the  wave  of  the  secondary 
current  must  necessarily  be  90°  behind 
the  wave  of  the  primary ;  but  instead  of 
that,  the  former  was  180°  behind  the  lat- 
ter, so  that  there  were  90°  extra  lag  in  a 
transformer.  The  same  result  had  been 
observed  by  Mr.  Blakesley  later  on,  and 
referred  to  in  a  paper  read  before  the 


154 

Physical  Society.*  He  did  not,  there- 
fore, think  that  the  arrangement  could 
be  taken  as  one  which  would  give  a  non- 
self-induction  in  the  external  circuit. 
The  author  had  stated  (p.  61),  "the 
coefficient  of  self-induction  was  found  to 
be  L  =  0.955  in  C.G.S.  measure,  and 
0.0955  in  practical  units."  C.G.S.,  of 
course,  meant  centimeter-gram-seconds ; 
what  "  practical "  units  were  he  did  not 
know.  If  they  were  the  ordinary  units 
of  self-induction,  corresponding  with  the 
true  ohm,  the  volt,  the  ampere,  and  so 
on — then  1  practical  unit  was  equal  to  109 
C.G.S.  units  or  centimeters.  The  number 
0.955  given  by  the  author  should  have 
been  divided  by  109  or  one  thousand 
million  ;  or  more  strictly,  in  consequence 
of  the  ohm  not  being  the  true  ohm,  the 
practical  unit  of  self-induction  was  99,777 
X  10*  centimeters.  Hence  the  coefficient 
of  self-induction  referred  to  by  the 
author  was  0.9571  X  10" 9  centimeters  in 
practical  units,  which  would  be  about 

'Proceedings  of  the  Physical  Society  of  London, 
1888,  vol.  ix.  p.  287. 


155 

6,200  miles.  Two  years  ago  Professor 
Perry  and  he  had  suggested  a  name  for 
the  practical  unit  of  self-induction,  it  not 
having  previously  received  any  name.  If 
the  practical  unit  were  exactly  a  thousand 
million  centimeters,  the  name  quadrant 
would  be  an  appropriate  one,  but  it  was 
about  ^  per  cent,  less  than  the  earth's 
quadrant,  and  they  had  therefore  sug- 
gested the  name  "  secohm "  (a  contrac- 
tion of  second  and  ohm).  Professor 
Ayrton  next  referred  to  a  standard  of 
self-induction  which  he  exhibited  on 
behalf  of  Professor  Perry  and  himself, 
and  which  he  thought  was  the  first  com- 
mercial standard  of  self  induction  ever 
issued.  It  consisted  of  two  coils  •  of 
platinoid  wire,  one  fixed  in  position,  and 
the  other  pivoted  so  that  it  could  be 
turned  about  a  diameter,  and  placed  in 
different  positions  relatively  to  the  fixed 
coil.  By  putting  the  coils  in  different 
positions  the  arrangement  had  different 
and  definite  coefficients  of  self-induction, 
the  values  of  which  were  indicated  on  the 
scale  in  secohms  from  0.013  to  0.036 


156 

secohm.  There  was  also  an  apparatus  on 
the  table  familiar  to  some  members,  called 
a  secohmmeter,  for  comparing  two  self- 
inductions.  It  rapidly  alternated  the 
battery  connections  and  the  galvanom- 
eter connections  of  a  Wheatstone's 
bridge,  and  it  rendered  the  measurement 
of  self-induction,  which  before  two  years 
ago  usually  had  been  very  un sensitive, 
having  had  to  be  effected  with  single 
impulses,  as  sensitive  as  the  ordinary 
measurement  of  resistance  with  a  Wheat- 
stone's  bridge.  With  a  combination  of 
those  two  instruments  the  coefficient  of 
self-induction  could  at  once  be  measured 
with  accuracy,  without  any  other  appa- 
ratus except  the  ordinary  Wheatstone's 
bridge.  Fig.  32  showed  symbolically 
the  arrangement  for  measuring  a  coeffi- 
cient of  self-induction  L2.  G  C  and  B  C 
were  the  galvanometer  and  battery  com- 
mutators of  the  secohmmeter,  which  were 
rotated  by  turning  the  handle  H.  Bal- 
ance for  steady  currents  having  been  first 
obtained,  the  secohmmeter  handle  was 
rotated  at  any  convenient  speed,  and  the 


157 

self- induction  L!  of  the  standard  adjusted 
until  balance  was  again  obtained,  when 

~  =  — .     The  continuous  lines  showed 
Lj         rx 

Fig.  32 


MEASUREMENT  OF  SELF-INDUCTION  WITH  SECOHM- 
METER  AND  SECOHJl  STANDARD. 

permanent  connections  in  the  secohm- 
meter,  and  the  dotted  lines  wires  em- 
ployed to  join  its  terminals  with  the 
Wheatstone's  bridge. 


158 

Mr.  T.  H.  Blakesley  said  that  the 
paper  had  considerable  breadth  ;  but,  like 
a  dangerous  piece  of  water,  it  was 
unequally  deep.  The  subject  was  a  very 
large  one,  and  perhaps  the  author  had 
not  been  able  entirely  to  do  justice  to  it, 
even  in  his  comparatively  long  paper. 
Mr.  Blakesley  had  himself  done  a  good 
deal  of  work  in  diagrams,  and  the  first 
remark  he  would  make  was  that  in  Figs. 
7,  8,  and  9,  the  direction  was  continually 
reversed.  In  Fig.  7  the  motion  of  the 
diagrams  was  supposed  to  be  clockwise, 
in  Fig.  8  it  was  the  reverse ;  and  in  Fig. 
9  it  was  supposed  to  be  the  same  as  in 
Fig.  7.  The  advantage  of  a  diagram 
of  that  kind  was  that  it  not  only  repre- 
sented the  magnitude  of  certain  quanti- 
ties of  electromotive  force  in  general,  but 
the  relative  positions  of  their  maximum 
value.  The  author  constantly  called  O 
A  the  current.  It  was  true  he  guarded 
himself  by  saying  that  it  was  propor- 
tional to  the  current  ;  but  those  who 
read  the  paper  might  suppose  that  he 
thought  O  A  to  be  in  phase  with  the 


159 

current.  It  was  not  so.  O  K  was  the 
real  effective  electromotive  force,  requir- 
ing mere  division  by  the  resistance  to 
represent  the  current,  as  in  ordinary 
steady  flow.  In  a  good  diagram,  it  only 

Fig.  33 


needed  a  pair  of  dividers  to  work  out 
results  which,  so  far  as  the  scale  allowedy 
were  as  complete  as  the  results  of  analysis. 
That  was  why  they  were  so  extremely 
valuable.  He  would  now  mention  the 
details  of  the  diagram  (Fig.  33)  with 


160 

a  view  of  fulfilling  the  characteristics 
which  he  had  mentioned,  and  which 
represented  all  cases  of  the  follow- 
ing problem  : — Given  two  alternate-cur- 
rent machines  coupled  in  series,  and 
having  given  electromotive  forces,  and 
the  same  known  period  of  alternation,  a 
given  resistance  in  the  whole  series  and 
a  given  coefficient  of  self-induction  for 
the  whole  series :  how  will  any  time- 
interval  between  the  corresponding 
phases  of  the  two  machines  (phase  angle), 
affect  (1)  The  work  to  be  put  into  the 
system  ;  (2)  The  work  to  be -got  out  of 
the  system ;  (3)  The  stability  of  the 
motion  ;  (4)  Efficiency  (or  the  relation  of 
(2)  to  (1));  (5)  the  work  wasted  in  heat- 
ing the  circuit  1  Proceed  thus  : — With 
a  pair  of  dividers  lay  down  to  any  con- 
venient scale,  A  B,  proportional  to  the 
electromotive  force  of  the  first  machine, 
and  B  C  (in  the  same  straight  line  but  in 
the  opposite  direction),  proportional  to 
that  of  the  second  machine,  and  describe 
a  circle  upon  A  B  as  diameter.  Adopt- 
ing as  the  positive  direction  of  ro- 


161 

tation  that  which  was  counter-clock- 
wise, set  off  the  angle  B  A  D  in  the 
negative  direction,  equal  to  that  of 

electric  lag  (Tan  B  A  D  =  =-^,  where 

-L     L\i 

L  =  the  coefficient  of  self-induction,  B 
— .  the  resistance  of  the  circuit,  and  T  = 
the  semi-period).  From  B  and  C  drop 
perpendiculars  upon  A  D,  cutting  it  in 
D  and  5  (not  given  in  Fig.  33  to  avoid 
confusion  of  lines).  D  would  obviously 
be  on  the  circle  already  drawn.  With  D 
as  center,  and  D  5  as  radius,  describe  a 
circle,  called  the  E-circle,  cutting  the 
former  circle  in  Q  and  E.  Then  all 
possible  phase-differences  between  the 
two  machines  might  be  represented  by 
some  angle  A  D  E,  where  E  was  always 
upon  the  E-circle.  For  any  point  E  the 
electromotive  forces  of  the  two  machines 
were  related  in  phase  and  magnitude, 
exactly  as  were  A  D,  D  E.  For  example, 
if  E  was  at  the  point  5,  the  phase-angle 
was  380°;  or  the  electromotive  force  of 
one  machine  was  throughout  its  varia- 
tions always  opposed  by  the  electromo- 


162 

tive  force  of  the  other.  Further,  if  for 
any  point  E,  A  E  was  joined  and  pro- 
duced, if  necessary,  to  cut  in  F  the 
circle  on  A  B  as  diameter,  the  values  of 
A  E,  E  F,  A  F,  could  be  taken  with 
the  dividers,  and  measured  on  the  scale 
first  employed.  These  lines  had  the 
following  properties  :  — 

If  R  was  the  resistance  of  the  circuit, 
then  — 

The  power  employed   on  )     _   A  E,  AF 

) 


the  first  machine  (input)  )  2  R 

The   p 

circuit 


The   power    heating   the  )  _  A  E2 
-      }         2  R  ' 


AE,EF 

employed  on  J       --  ^p  —  • 

the  second  machine  - 
The  latter  depending  on  whether  E  lay 
within  or  without  the  circle  upon  A  B. 
If  E  lay  within  the  circle  upon  A  B, 
work  would  be  given  out  by  the  second 
machine  ;  that  was,  it  might  be  employed 
as  a  motor.  If,  on  the  other  hand,  E 
lay  upon  that  portion  of  the  E-cir- 
cle  without  the  circle  upon  A  B, 
power  must  be  employed  on  the  second 


163 

machine  from  outside,  and  it  would  do 
part  of  the  work  of  heating  the  circuit. 
Thus  the  two  problems,  of  transmission 
of  power  and  working  in  series,  were 
really  parts  of  the  same  general  problem. 
The  points  Q  and  B  were  the  positions  of 
E  where  these  problems  passed  one  into 
the  other,  namely,  where  the  output  was 
zero.  Through  D  draw  a  diameter  to  the 
E  circle  parallel  to  A  B,  or  3  D  4,  and  a 
second  diameter  through  K,  the  bisection 
of  A  B,  or  2  D  K  1.  It  would  be  seen 
that  these  two  diameters  were  equally 
inclined  to  A  D.  The  points  upon  the 
E-circle  so  obtained  had  the  following 
peculiarities : — If  E  coincided  with  1,  the 
maximum  power  would  be  given  out  by 
the  second  machine;  if  E  coincided  with 
2,  the  maximum  power  existed  which 
could  be  employed  upon  the  second 
machine ;  if  E  coincided  with  3,  the  mini- 
mum power  existed  of  the  first  machine  ; 
if  E  coincided  with  4,  the  maximum 
power  existed  of  the  first  machine.  Fur- 
ther, if  E  lay  upon  the  semi-circle  1  Q  2, 
there  was  stability  for  the  second 


164 

machine ;  and  if  E  lay  upon  the  semi- 
circle 2  E  1,  there  was  instability  for  the 
second  machine ;  if  E  lay  upon  the  semi- 
circle 324,  there  was  instability  for  the 
first  machine ;  and  if  E  lay  upon  the 
semi-circle  4,  1,  3,  there  was  stability  for 
the  first  machine.  Thus  the  region  1,  5? 
3,  had  a  double  guarantee  of  stability. 
The  angle  1  D  3  was  twice  that  of 
electric  lag ;  which  showed  one  of  the 
advantages  of  self-induction.  Again,  if  a 
line  from  A  to  4  cut  the  E-circle  in  6, 
this  would  be  the  point  for  E  giving 
the  maximum  efficiency  in  the  trans- 
mission of  power.  It  must  lie  in  the 
region  of  stability.  The  point  5  had 
the  property  that  the  efficiency  there 
had  the  ratio  of  the  two  electromotive 
forces,  as  in  the  case  of  steady  cur- 
rents, but  it  was  not  as  great  at  5  as 
at  6.  Fig.  34  had  been  constructed  in  the 
same  way  as  Fig.  33,  and  with  the  same 
electromotive  forces,  but  with  a  larger 
angle  of  electric  lag  BAD.  It  was 
intended  to  show  by  an  example  that 
the  point  3  did  not  necessarily  lie  within 


165 

the  circle  upon  A  B.  If  circumstances 
were  as  in  Fig.  34,  then  E  might  come 
between  3  and  Q,  and  be  outside  the 
circle  upon  A  B.  Thus  there  would  be, 
for  such  a  point,  stability  for  both 
machines  at  the  same  time  that  both 

Fig.  34 


machines  would  take  part  in  heating  the 
circuit.  The  possibility  of  such  an 
arrangement  had  been  denied  by  Dr. 
Hopkinson  in  this  Institution,  and  wide 
currency  had  been  given  to  his  statement. 
It  should  be  distinctly  understood  that 
the  statement  was  not  one  of  general 


166 

truth,  and  with  short  periods  and  large 
self-induction,  two  machines  in  series 
might  easily  be  run  to  work  with 
stability.  He  had  only  been  able  to  indi- 
cate the  use  of  such  diagrams  as  he 
recommended.  A  very  slight  addition  to 
the  diagrams  enabled  the  effect  of  hys- 
teresis to  be  taken  into  account.  Hyster- 
esis was  the  work  absorbed  in  the  magnet- 
ized masses  in  the  field,  upon  change 
taking  place  in  the  degree  or  direction  of 
magnetization.  This  was  now  a  recog- 
nized fact,  and  well-known  measurements 
of  the  effect  had.  been  made  by  Dr. 
Ewing  and  others.  On  the  subject  of 
transformers,  he  might  mention  a  system 
of  transformation  which  might  be 
usefully  employed  in  many  practical 
ways.  Suppose  that  an  alternate- current 
machine  (Fig.  35)  played  into  a  con- 
ductor possessing,  besides  resistance, 
various  causes  of  self-induction.  And 
suppose  that  at  two  points  A,  B,  of  the 
circuit  were  coupled  the  poles  of  a  con- 
denser. Then  in  general  it  would  be 
found  that :  (1)  The  relative  values  of 


167 

the  current,  in  the  sections  near  the 
machine  and  remote  from  it,  became 
changed  from  unity,  which  was,  of  course, 
the  relation  before  the  introduction  of 
the  condenser :  (2)  There  arose  a  differ- 
ence in  phase  in  the  two  portions  of  the 
circuit.  Both  these  changes  depended 
only  upon :  (i)  the  coefficient  of  self-in- 
duction in  the  remote  section  only ;  (ii) 
the  resistance  in  the  remote  section  only; 

Fig.  35 


(iii)  the  capacity  of  the  condenser ;  (iv) 
the  period ;  and  not  upon  the  coefficient 
of  self  induction,  or  the  resistance  of  the 
section  near  the  generator,  or  of  the 
generator  itself.  Under  a  proper  arrange- 
ment of  the  four  properties  quoted,  a 
considerable  excess  of  current  could  be 
easily  effected  in  the  remote  section  over 
that  in  the  nearer  section.  Mr.  Nalder 
had  been  kind  enough  to  give  him  the 


168 

opportunity  to  test  the  results  of  the 
theory  in  practice,  and  he  supposed  they 
were  the  first  people  to  see,  so  far  as 
it  was  possible  by  means  of  a  dyna- 
mometer to  do  so,  a  current  in  one 
conductor  at  some  distance  from  the 
generating  machine  very  much  in  excess 
of  its  value  at  points  near  to  and  in 
the  machine  itself.  Not  merely  could 
such  a  transformation  in  relative  magni- 
tude be  effected,  but  the  phase  rela- 
tion could  be  adjusted,  thus  giving  the 
method  very  wide  applicability.  For  in- 
stance, the  two  portions  of  the  circuit 
could  have  their  phases  thrown  into  quad- 
rature with  each  other ;  while  the  values 
might  be  kept  equal,  which  was  the  condi- 
tion of  things  desirable  in  the  Tesla 
motor,  now  obtained,  as  Professor  Ayrton 
had  said,  by  two  circuits. 

Captain  P.  Car  dew,  R.  E.,  said  that  in 
the  paper  the  reasoning  was  based  upon 
the  usual  assumption  that  the  varying 
quantities,  magnetic  induction,  electro- 
motive force,  and  current,  followed  the 
sinusoidal  curve.  That  was  admittedly 


169 

on]y  an  approximation  for  the  purpose 
of  facilitating  the  calculations.  It  was 
probably  nearly  true  in  the  case  of  ma- 
chines with  no  iron  in  the  generative 
portion,  or  armature,  in  which  a  copper 
conductor  was  dragged  through  alter- 
nating magnetic  fields ;  but,  in  the  case 
of  machines  in  which  the  armature  wires 

Fig.  36 


were  coiled  on  iron  cores,  the  electro- 
motive force  being  due  to  the  variation 
of  induction  in  those  cores,  he  did  not 
think  that  law  of  variation  could  hold. 
The  maximum  induction  in  the  moving 
iron  was  not  reached  until  after  the  point 
of  nearest  approach  to  the  fixed  magnet 
had  been  passed.  When  once  the  lines 


170 

of  force  had  begun  to  clear  out  of  the 
iron,  the  action  would  go  on  rapidly,  in 
spite  of  the  opposing  action  of  the  in- 
duced current,  owing  to  the  molecules  of 
iron  assisting  the  demagnetization,  the 
curve  of  induction  being  something  like 
the  firm  line,  while  the  curves  of  current 
were  like  the  dotted  line  in  Fig.  36.  In 
the  same  way,  if  the  moving  iron  was 
whirled  past  alternating  polarities,  the 
curves  of  induction  and  of  current  would 
still  be  unsymmetrical  and  unsymmetric- 
ally  disposed  with  regard  to  the  times  of 
coincidence  of  the  axes  of  the  fixed  and 
moving  magnets  (Fig.  37). 

Mr.  W.  M.  Mordey  was  glad  the  author 
had  adopted  his  term  "  Alternator."  The 
old  term  "  alternating- current  dynamo- 
electric  machine"  was  very  cumbrous. 
Alternators  might  be  divided  into  two 
classes,  those  which  had  iron  in  the  arma- 
tures, and  those  which  had  not.  As  his 
own  machine,  made  by  the  Brush  Corpora- 
tion, and  that  of  Ferranti,  were  the  only 
examples  of  the  latter  class  described 
by  the  author,  he  might  be  permitted 


171 

to  mention  the  reasons  which  had  led 
him  to  avoid  the  use  of  iron.  He  thought 
that  makers  of  dynamos  would  agree  that 
almost  all  the  ills  that  the  dynamo  was 
heir  to  were  due  to  the  presence  of  the 
iron  in  the  armature.  Its  use  in  direct- 
current  machines  might  be  said  to  be  a 

Fig.  37 


necessary  evil,  as,  although  attempts  had 
been  made  to  do  without  it,  all  successful 
types  of  such  machines  required  it  for 
structural  purposes.  Iron  in  armatures 
when  worked  at  a  high  magnetic  density, 
and  with  rapid  reversals  or  variations  of 
magnetisms,  became  heated,  and  wasted 
a  good  deal  of  power.  In  alternators 
this  objection  applied  with  very  much 


172 

greater  force  than  in  direct- current  ma- 
chines, for  in  the  latter  the  reversals 
of  magnetism  were  comparatively  slow. 
Thus  the  first  result  arrived  at,  in  quite 
recent  practice,  was  that  the  magnetic 
density  that  could  be  used  in  iron  cored 
alternators  must  only  be  about  one-half 
that  employed  in  direct  current  arma- 
tures. This  alone  meant  a  considerable 
increase  in  the  size  of  armatures, 
without  any  gain  in.  output  or  efficiency. 
Although  the  loss  per  cubic  inch  was 
reduced  by  decreasing  the  magnetic  den- 
sity, the  armature  had  to  be  made  larger 
to  compensate  for  it,  and  the  total  loss 
was  actually  increased,  not  reduced.  Iron 
was  used  to  reduce  the  magnetic  resist- 
ance, to  afford  mechanical  support,  and 
to  introduce  self-induction  into  the  cir- 
cuit. The  latter,  an  evil  in  itself,  was 
said  to  be  a  modern  necessity,  caused  by 
the  convenience  of  working  alternators 
in  parallel.  If  iron  was  indispensable 
for  this  purpose,  which  he  was  not 
prepared  to  admit,  it  could  readily  be 
inserted  in  some  part  of  the  circuit  where 


173 

ample  space  and  cooling  surface  could  be 
provided,  and  from  which  it  could  be 
easily  removed  when  not  required,  that 
was  when  it  was  only  necessary  to  run 
one  machine.  The  armature  was  the 
very  worst  place  for  iron.  He  ventured 
to  think  it  was  much  the  best  to  make 
the  armature  stationary,  as  he  had  done. 
It  then  had  only  to  resist  the  tangential 
drag  of  the  field.  He  thought  a  great 
mistake  was  made  in  some  alternators  in 
using  Pacinotti  projections.  In  all  cases 
there  should  be,  as  nearly  as  possible,  a 
steady  magnetic  flux  in  the  field.  This 
could  not  be  done  if  projections  were 
used.  The  Zipernowsky  and  Parsons 
machines  were  faulty  in  this  respect. 
Much  had  been  said  about  the  form  of 
the  wave  yielded  by  alternators.  He  had 
some  time  ago  made  an  experiment  with 
the  first  of  his  machines,  using  the 
method  which  was  now  described  by 
Professor  Ayrton,  and  found  that  the 
curve  had  the  form  shown  by  Fig.  38, 
which  was  almost  a  sine-curve.  On  the 
subject  of  the  lag  in  transformers,  to 


174 

which  Professor  Ayrton  had  also  alluded, 
he  might  be  allowed  to  mention  that,  in 
the  discussion  of  another  paper  by  the 
author,  he  had  first  stated  the  fact,*  and 
had  described  a  simple  experiment,  show- 
ing that  the  primary  and  secondary  cur- 
rents reached  their  maxima  and  minima 
practically  at  the  same  time. 

Sir  James  N.  Douglass  considered  that 
the  discussion  had  thrown  a  considerable 
amount  of  light  on  the  relative  advan- 
tages of  direct  and  alternate-current  ma- 
chines for  lighting  and  power  purposes. 
In  1862  the  French  lighthouse  authori- 
ties adopted  the  alternate-current  machine 
of  the  Alliance  Company  at  the  two  light- 
houses of  Cape  la  Heve;  and  in  1866, 
Holmes  produced  his  alternate-current 
machine,  and  a  pair  of  these  were  made 
for  the  Trinity  House  and  exhibited  at 
the  Paris  International  Exhibition  of 
1867.  These  machines  were  installed  at 
the  Souter  Point  Lighthouse  in  1870, 
where  they  had  worked  regularly  and 

*  Journal  of  the  Institution  of  Electrical  Engineers, 
vol.  xvii.,  p.  215. 


175 

efficiently  ever  since,  and  without  a  single 
failure  or  the  necessity  for  any  repair. 
In  1877,  the  Trinity  House  made  a  series 
of  competitive  trials  at  the  South  Fore- 
land, with  the  Holmes  and  Alliance  alter- 
nating, and  the  more  powerful  direct-cur- 

Fig.  38 


MORDEY- VICTORIA  ALTERNATOR.  OPEN  CIRCUIT  CURVE 
OF  INDUCTION,  HALF  PERIOD.  THE  DOTTED  LINE 
IS  A  SINE-CURVE. 

rent  machines  of  Gramme  and  Siemens, 
which  resulted  in  the  adoption  of  the 
Siemens  machines  for  the  two  Lizard 
lighthouses  in  1878.  In  1879,  the  alter- 
nate-current machine  of  Baron  de  Meri- 


176 

tens  was  tested  at  the  Royarinstitution 
by  Dr.  Tyndall  and  himself,  and  one  was 
purchased  by  the  Trinity  House  in  1880, 
and  sent  to  the  Lizard  lighthouses,  where 
it  had  been  in  successful  operation  every 
night  since  that  date,  giving  no  more 
trouble  than  the  original  alternate-cur- 
rent machines  of  the  Alliance  Company 
and  Holmes.  Three  of  these  machines 
of  larger  size,  giving 'currents  of  about 
160  amperes  and  42  volts,  were  purchased 
by  the  Trinity  House,  and  used  at  the 
trials,  at  the  South  Foreland,  in  1884-85, 
into  the  relative  merits  of  electricity,  gas, 
and  mineral  oil  as  lighthouse  illuminants. 
These  machines  gave  great  satisfaction, 
and  two  of  them  had  since  been  perma- 
nently installed  at  St.  Catharine's  light- 
house. 

Mr.  G.  Kapp,  in  reply,  said  he  had 
first  thought  that  his  paper  was  more 
scientific  than  it  should  have  been,  but 
the  discussion  had  beaten  him  completely 
in  the  amount  of  science  which  had  been 
developed.  Considerable  importance 
seemed  to  have  been  attached  to  the 


177 

nomenclature  in  the  paper.  Whether  a 
certain  electromotive  force  should  be 
called  "  mean,"  "  average,"  "  equivalent," 
the  "square  root  of  the  mean  squares," 
or  by  any  other  name,  might  be  a  fit  sub- 
ject for  discussion  from  a  pure  academic 
point  of  view,  but  practical  engineers 
were  satisfied  with  the  terms  ordinarily 
in  use,  provided  definitions  were  added 
to  prevent  misunderstanding.  The  dia- 
grams had  not  been  designed  with  a  view 
of  finding  out  everything  which  could 
possibly  be  ascertained  about  alternators, 
but  simply  as  mental  tools,  perfected 
only  so  far  as  necessary  for  the  work  of 
designing  alternators,  but  not  further. 
The  statement  in  the  paper,  that  there 
was  no  self-induction  in  a  bank  of  trans- 
formers working  glow-lamps,  although 
described  as  incorrect  by  Professor  Ayr- 
ton,  had  in  reality  been  confirmed  by  the 
remarks  that  gentleman  had  made,  and 
also  by  what  fell  from  Mr.  Mordey.  Both 
had  said  virtually  the  same  thing,  namely, 
that  the  lag  was  nearly  180°  between  the 
phases  of  primary  and  secondary  current. 


178 

But  the  lag  between  the  induced  counter 
electromotive  force  in  the  primary  and 
the  secondary  current  was  also  180°, 
and  therefore  the  phases  of  terminal 
electromotive  force,  induced  electromo- 
tive force,  and  current  in  the  primary, 
must  very  nearly  coincide,  which  was 
only  possible  if  there  was  practically  no 
self  induction.  He  wished  to  offer  an 
explanation  with  regard  to  the  units  used 
in  the  paper.  His  reason  for  adopting 
these  units  was  that  they  were  convenient, 
and  since  he  first  brought  them  forward 
many  others  had  adopted  them.  All 
knew  that  the  scientifically  correct  unit 
was  inconvenient  for  the  shop,  and  as 
the  object  of  practical  engineers  was  to 
build  machines  in  the  easiest  way,  he  had 
adopted  that  system  of  units  which  many 
years'  practice  had  shown  him  to  be  the 
most  convenient.  Professor  Forbes  had 
objected  to  the  parallel  working  of  dyna- 
mos, chiefly  on  the  ground  that  it  was 
necessary  to  cut  out  certain  districts  in 
case  of  fire.  Mains  might  be  joined  in 
parallel  at  the  stations,  but  they  need  not 


179 

be  joined  outside  where  the  fire  might 
occur.  There  was  no  objection  to  work- 
ing all  the  circuits  from  a  pair  of  omnibus 
bars  in  the  station,  but  they  should  be 
disconnected  in  the  districts  to  be  lighted. 
Another  objection  urged  was  the  drop  of 
external  pressure  with  an  increase  of 
current,  provided  the  exciting  current 
was  not  varied.  That  was  a  serious 
objection  when  there  was  one  dynamo 
machine  only  at  work,  and  when  a  large 
part  of  the  total  load  would,  on  certain 
occasions,  be  taken  off  suddenly.  For 
example,  in  ship-lighting  it  often  hap- 
pened that  the  lamps  were  divided  be- 
tween a  few  circuits,  and  a  large  number 
of  lamps  must  thus  be  switched  off  at 
one  instant.  This  would,  with  an  alter- 
nator having  a  large  self-induction,  pro- 
duce in  the  remaining  lamps  a  great 
jump.  But  these  machines  were  not 
intended  for  ship-lighting  or  small  iso- 
lated installations ;  they  were  intended 
for  large  central  stations  where  there 
were  many  thousand  lamps,  and  where 
the  effect  of  switching  on  or  off  even  as 


180 

many  as  one  hundred  lamps  simultane- 
ously would  be  infinitesimal  in  compari- 
son with  the  large  number  of  lamps 
alight.  He  did  not  think  that  a  switch 
that  contained  mercury  troughs  which 
would  bob  up  and  down  was  as  good 
as  a  switch  with  solid  contacts.  The 
switches  used  at  the  Grosvenor  Gallery 
were  of  the  latter  type,  and  in  his  opinion 
far  superior  to  the  mercury  switches 
which  Professor  Forbes  had  praised  so 
much.  Professor  Forbes  was  a  little  too 
severe  on  English  engineers  when  he 
said  that  they  merely  copied  foreign 
dynamos.  It  was  quite  true  that  in  a 
certain  sense  all  machines  resembled 
each  other,  in  so  far  namely  as  all  con- 
tained field-magnets  and  an  armature ; 
but  this  was  also  the  case  with  continu- 
ous-current dynamos,  of  which  many 
different  types  were  nevertheless  recog- 
nized. He  did  not  think  high  frequency 
was  objectionable  on  the  ground  of 
parallel  working,  but  it  was  on  the 
grounds  which  he  had  mentioned  in  the 
paper.  He  was  sorry  Professor  Forbes 


181 

had  found  fault  with  the  transformers 
made  in  England.  He  appeared  to  have 
a  low  opinion  of  English  engineers  since 
he  had  seen  some  of  the  central  stations 
on  the  Continent.  His  contention  was 
that  in  England  electricians  were  employ- 
ing too  long  a  magnetic  circuit.  But 
all  these  transformers  which  Professor 
Forbes  criticised  adversely  were  not 
made  yesterday;  they  were  begun  to  be 
made  three  years  ago.  Many  hundreds 
were  at  work,  and  they  had  been  altered 
and  altered  till  the  present  forms  had 
been  developed.  The  magnetic  circuit 
was  long,  but  the  electric  circuit  was 
short,  and  a  short  electric  circuit  was  far 
more  important  than  a  short  magnetic 
circuit.  As  a  matter  of  fact,  even  the 
.  Zipernowsky  transformer,  which  Pro- 
fessor Forbes  admired  so  much,  had  a 
long  magnetic  circuit.  Three  or  four 
years  ago,  at  the  Inventions  Exhibition, 
that  wonderful  transformer  with  a  spe- 
cially short  magnetic  circuit  was  first 
seen.  It  was  a  Gramme  ring  turned 
inside  out.  It  was  stated  to  be  a  mar- 


182 

velous    improvement;    but    not    one   of 
those  transformers  was  now  at  work ;  all 
had   been   exchanged    for   the   ordinary 
Gramme  ring,  with  iron  inside  and  cop- 
per  outside,  because   in   this   form  the 
electric  circuit  was  short ;  consequently, 
the  regulating  power  of  the  transformer 
was  better  than  it  had  been  previously. 
The  other  question  raised  about   trans- 
formers  was  whether  a  high   or   a   low 
frequency   was   advantageous.     A  fairly 
high  frequency  was  advisable ;  but  above 
a  certain  limit,  say  70  complete  periods 
per  second,  an  increase  of  frequency  did 
not  reduce  the  size  of  the  transformer. 
On  the  table  there  was  one  of  his  transfor- 
mers, weighing  200  Ibe.,  and  feeding  fifty 
lamps,  giving  a  weight  of  4  Ibs.  per  lamp. 
It  was  built  for  a  frequency  of  70.     The 
Westinghouse    transformer   (taking   the 
figures  from  a  paper  by  Professor  Forbes 
at  the  last  meeting  of  the  British  Associa- 
tion) was  for  forty  lamps,  and  it  weighed 
160  Ibs.,  or  4  Ibs.   per  lamp.     In   that 
case  the  frequency  was  133   as  against 
his   70.     That    was    a    proof    that    the 


183 

increase  of  frequency  did  not  diminish 
the  weight  of  the  transformers.  Pro- 
fessor Forbes  had  brought  a  diagram 
showing  the  output  from  the  Grosvenor 
Station  (Fig.  28),  and  he  argued  that  the 
transformers  by  themselves  absorbed  an 
energy  equal  to  four  thousand  lamps. 
That  was  surely  not  to  be  taken  as  a 
serious  argument.  The  diagram  was  not 
one  of  HP.,  but  one  of  current  sent  out. 
Now  the  current  sent  out  of  course 
depended  on  the  lamps  which  were 
alight.  The  argument  was  that  in  the 
early  hours  of  the  morning  there  were 
no  lamps  on  circuit.  But  that  was  not 
so  certain.  In  the  case  of  stations  sup- 
plying electric  light  by  contract,  for  a. 
fixed  rental  without  a  meter,  people  were 
wasteful  with  the  lamps  and  allowed  them 
to  burn  all  night  long.  Professor  Forbes 
had  overlooked  one  important  circum- 
stance, namely,  that  if  the  transformers 
were  on  the  circuit  without  giving  off 
current  to  the  lamps,  there  was  a  lag  of 
70°,  80°  or  more  between  the  terminal 
electromotive  force  and  the  primary  cur- 


184 

rent  in  each  transformer.  The  energy 
must  therefore  not  be  taken  as  repre- 
sented by  the  product  of  electromotive 
force  and  current,  as  given  in  the  diagram, 
but  by  this  product  multiplied  by  the 
cosine  of  the  angle  of  lag.  On  purely 
theoretical  grounds  all  the  transformers 
now  in  use  were  equally  good  and  their 
efficiency  was  high.  Professor  Ayrton 
had  tested  some,  and  found  that  it  was 
as  high  as  95  per  cent.  The  difference 
in  the  transformers  was  in  their  details, 
such  as  would  secure  low  first  cost, 
facility  of  manufacture,  ease  of  changing 
a  coil,  freedom  from  humming,  ability  to 
keep  cool,  and,  above  all  things,  absolute 
safety  of  insulation. 


COEKESPONDENCE. 

Mr.  J.  D.  F.  Andrews,  in  reference  to 
the  author's  observations  on  eddy  cur- 
rents (p.  64),  and  his  inability  "to 
suggest  an  entirely  satisfactory  explana- 
tion for  the  effect  of  the  iron  core  in 


185      . 

reducing  eddy  currents  in  the  copper," 
stated  that  he  had  contributed  the  results 
of  a  series  of  experiments  in  a  letter  to 
Industries,*  in  which  he  showed  that  the 
strength  or  amount  of  eddy  currents 
depended  on  the  speed  with  which  the 
wire  moved  into  and  out  of  the  magnetic 
field,  and  that  they  could  be  greatly 
reduced  by  shaping  the  magnet-poles  so 
that  the  wire  gradually  entered  and  left 
the  field.  The  shape  of  the  conductor, 
and  its  position  relative  to  the  armature 
core  and  the  field-magnets,  had  a  greater 
bearing  on  the  reduction  of  eddy  currents 
than  the  shape  of  the  field- magnets ;  and 
round  wire  of  any  diameter  was  nearly 
proof  against  eddy  currents  if  the 
machine  was  otherwise  correctly  propor- 
tioned. 

Mr.  A.  Du  Bois-Keymond  remarked 
that  some  minor  points  in  the  diagrams 
seemed  open  to  criticism.  With  regard 
to  Figs.  9  and  10,  he  could  not  fully 
comprehend  the  author's  meaning  when 
he  said,  u  the  length  O  A,  that  is  to  say, 

*  Vol.  iv.   1888,  p.    M9. 


186 

the  current,"  and  accordingly  defined  the 
mechanical  output  of  the  machine  as 
"  the  product  O  A  and  O  D."  As  far  as 
he  could  make  out,  O  A  was  the  resultant 
electromotive  force  obtained  by  the 
.addition  of  the  terminal  and  induced 
electromotive  forces  Et  and  E,  and  by  the 
author's  own  showing  (Fig.  7)  the  current 
ought  to  be  the  resultant  of  this  and  of 
the  electromotive  force  due  to  self-indue" 
tion,  that  was,  it  ought  to  coincide  with 
O  K ;  or  assuming  the  terminal  resistance 
to  be  one,  it  would  be  equal  to  O  K. 
Accordingly,  the  mechanical  work  gener- 
ated would  be  the  product  of  O  E  and  O 
D,  namely,  E.  I.  cos  B  O  F,  I  standing 
for  the  current.  Moreover,  he  should 
prefer  assuming  some  definite  position  of 
Et  to  start  from  as  being  more  conforma- 
ble to  reality,  aud  letting  E  shift  about, 
thereby  altering  the  positions  and  magni- 
tudes of  the  other  quantities.  There 
would  then  be  perfect  agreement  between 
the  author's  diagram  and  the  geometrical 
solution  of  the  same  problem  explained 
by  him  in  a  paper,  "  On  the  difficulties  in 


187 

the  way  of  transmitting  power  by  alter- 
nating currents."*  The  use  to  which  the 
author  put  the  diagrams,  namely,  to 
determine  the  safety  of  running  a  given 
machine  in  parallel  with  others,  was 
admirable,  and  quite  put  an  end  to  the 
doubts  hitherto  entertained  by  practi- 
tioners on  this  head. 

Professor  J.  A.  Ewing  said  that  at  p. 
65  of  the  paper  there  was  a  remark 
about  the  dissipation  of  energy  in  the 
armatures  of  dynamos  through  magnetic 
hysteresis,  from  which  it  seemed  to 
him  that  the  author  had  perhaps  some- 
what misunderstood  in  one  respect  the 
position  he  had  taken  up  in  the  paper 
there  referred  to.  What  he  had  shown 
was  that  the  energy  dissipated  in  iron, 
through  magnetic  hysteresis  in  reversals 
of  magnetism,  might  be  very  much 
reduced  if  the  metal  were  subjected  to 
vibration  during  the  process.  When  a 
soft  iron  wire,  for  example,  was  sharply 


*  The  Telegraphic  Journal  and  Electrical  Review 
vol.  xxiv.  1889,  p.  112;  and  Elektrotechnische  Zeitschrift 
vol»  x.  1889,  p.  1. 


188 

tapped  during  repeated  reversals  of  its 
magnetism,  there  was  practically  no  dissi- 
pation of  energy  through  hysteresis,  and 
even  a  very  slight  mechanical  disturbance 
had  some  influence  in  reducing  the  dissi- 
pation. In  applying  this  result  to 
dynamos,  all  tthat  he  had  said  was  this  : 
"  Hence,  in  a  dynamo,  where  vibration 
occurs  to  a  greater  or  less  degree  when- 
ever the  machine  is  running,  the  energy 
dissipated  through  changes  of  magnetiza- 
tion is  even  less  than  these  experiments 
on  still  metal  would  lead  us  to  expect."* 
He  had  meant,  in  these  words,  to  draw 
attention  to  the  fact  that  whatever  vibra- 
tion occurred  in  the  armature  of  a 
dynamo  would  tend  to  lessen  the  dissipa- 
tion of  energy,  produced  by  hysteresis? 
below  the  value  measured  by  his  experi- 
ments on  still  metal.  He  had  not  meant 
to  suggest  that  any  large  effect  of  this 
kind  was  actually  produced,  and  in  fact 
he  agreed  with  the  author  in  believing 
that  in  a  well-balanced  dynamo  the  vibra- 
tion was  not  likely  to  be  seriously  influen- 

*  Phil.  Trans.  Royal    Society,  1885,  p.  554.   • 


189 

tial,  so  that  the  values  of  the  dissipation 
calculated  from  his  experiments  were 
probably  not  too  high  for  application  to 
such  a  case.  With  reference  to  "  viscous 
hysteresis "  (p.  67),  he  had  made  no 
direct  observations  showing  that  the 
energy  dissipated  through  hysteresis 
increased  -  with  the  speed  at  which  the 
cyclic  change  of  induction  was  performed. 
So  far  as  any  such  observations  had 
been  made,,  he  understood  that  the 
results  had  been  negative,  and  that  the 
heating  effect  per  cycle  had  been  sensibly 
the  same  whether  the  same  cycle  was 
repeated  with  greater  or  with  less 
frequency.  But  there  was  a  certain 
amount  of  evidence  that  magnetization 
took  some  time  to  be  fully  developed  in 
iron  after  the  magnetizing  force  was 
applied,  especially  when  the  magnetizing 
force  was  low,  and  so  far  as  this  was  true 
it  must  have  the  effect  of  increasing  the 
dissipation  of  energy  in  cycles  of  high 
frequency,  since  larger  changes  of  mag- 
netic force  would  then  be  required  to 
produce  equal  changes  of  magnetic 
induction. 


190 

Dr.  John  Hopkinson  said  that  one  of 
the  questions  with  which  the  author 
dealt  was  how  many  alternations  per 
second  was  it  most  appropriate  to  use  for 
distribution  by  transformers'?  It  was 
clear  that  the  answer  depended  upon  a 
balance  of  advantages.  No  one  would 
use  exceedingly  few  alternations  ;  no  one 
would  advocate  a  greater  number  than 
some  superior  limit  much  less  than  the 
greatest  it  was  possible  to  produce.  In 
favor  of  a  high  frequency  was  the  fact 
that,  for  a  given  efficiency,  the  trans- 
former would  be  cheaper  to  manufacture. 
On  the  other  hand,  in  favor  of  a  low 
frequency,  the  whole  of  the  conductor 
was  not  equally  used  with  alternating 
currents.  The  author  had  alluded  to  the 
question  of  a  viscous  hysteresis  in  mag- 
netization of  iron.  Dr.  Hopkinson 
doubted  the  propriety  of  the  term  vis- 
cous hysteresis,  but  he  knew  what  was 
meant.  There  was,  he  believed,  no  satis- 
factory evidence  of  the  existence  of  so- 
callecl  viscous  hysteresis,  and  it  was 
certainly  a  phenomenon  by  no  means  so 


191 

marked  as  true  hysteresis  when  the 
magnetism  of  iron  was  reversed.  In  his 
lecture  before  the  Institution  in  1883,  he 
not  only  explained  why  alternate- current 
machines  could  be  run  parallel  but  also 
mentioned  that  an  alternate-current 
machine  could  be  run  as  a  motor.  The 
theory  of  both  cases  had  been  fully 
developed  by  himself  in  a  paper  read 
before  the  Society  of  Telegraph  En- 
gineers ;*  and,  at  his  suggestion,  Pro- 
fessor Adams  successfully  tried  the 
experiment  of  running  a  machine  as  a 
motor  at  the  South  Foreland.  In  1887 
he  presented  to  the  Royal  Society  two 
short  papers. f  The  first  related  to  trans- 
formers, and  showed  how  to  treat  them, 
taking  proper  account  of  the  true  mag- 
netic properties  of  the  iron.  The  second 
treated  the  theory  of  alternate-current 
machines  ;  showed  how  the  true  differ- 
ential equation  of  currents  could  be 


*  Journal  of  the  Society  of  Telegraph  Engineers 
and  Electricians,  vol.  xiii.  1884,  p.  496. 

t  Proceedings  of  the  Royal  Society,  vol.  xlii.  H-. 
164  and  167. 


192 

obtained,  and  that  it  differed  materially, 
in  some  cases,  from  the  linear  equation 
generally  used,  but  was  of  a  character 
not  convenient  for  practical  use. 

Mr.  Elihu  Thomson,  in  regard  to  the 
relation  between  the  width  of  the  field- 
poles  and  the  armature-winding,  observed 
that  the  author's  statement  that  "  width 
of  poles  equal  to  half  the  pitch,  smooth 
armature,  and  winding  covering  only  one- 
half  the  surface,"  was  most  frequently 
met  with  in  practice,  was  without  doubt 
true.  But  was  it  the  best  practice  ? 
While  designing  such  machinery,  it  oc- 
curred to  him  that  a  higher  yield  in 
electromotive  force  would  be  had  from  a 
given  armature,  particularly  under  full 
load,  or  "dynamic"  working,  as  dis 
tinguished  from  open  circuit,  or  "  static  " 
condition,  if  the  open  space  in  the 
interior  of  each  coil  was  made  less  than 
the  width  of  the  pole-face.  It  was  seen 
that  this  must  result  as  a  consequence  of 
the  crowding  or  distortion  of  the  field- 
lines  forward  by  the  currents  in  the 
armature-coils,  having  the  practical  effect 


193 

of  somewhat  narrowing  the  effective  pole- 
face  presented  to  the  armature.  A  trial 
machine  was  built,  on  the  type  in  use  by 
the  Thomson-Houston  Electric  Company, 
which  consisted  of  a  field  structure  with 
inward  radial  cores  and  a  cylindrical 
armature  with  very  flat  coils  laid  on  and 
bound  down,  their  curved  ends  out  of 
the  field;  not,  however,  being  turned 
down  toward  the  shaft,  as  is  the  case 

Fig.  39 


with  the  Westinghouse  machine.  The 
field-poles  had  a  width  approximately 
equal  to  one  half  the  pitch,  the  armature 
being  smooth.  In  the  trial  machine  the 
coils  were  laid  on  so  as  to  practically  cover 
the  whole  exterior  of  the  armature- core,  or 
they  were  wound  with  but  a  narrow  line 
of  open  space  in  the  center  of  each  coil, 


194 

as  in  Fig.  39.  Arrangements  were  made 
that  the  inner  turns  might  be  progress- 
ively cut  out,  so  as  to  virtually  remove 
wire  from  each  coil.  Under  static  condi- 
tion, or  no  load,  the  terminal  electromo- 
tive force  was  practically  unchanged, 
even  though  considerable  fractions  of 
wire-turns  were  cut  out  from  the  center 
of  each  coil.  But  under  a  load  a  limit 
was  soon  found,  or  a  point  reached,  in 
which  the  electromotive  force  was  the 
maximum  under  a  given  excitation  of  the 
field.  This  maximum  was  reached  after 
a  few  turns  had  been  removed  or  cut 
out ;  and  the  open  space  in  the  center  of 
the  coil  so  obtained  was  adopted  for  use 
in  the  apparatus  subsequently  manufact- 
ured on  the  large  scale.  The  vacant 
space  was  less  than  one-half  the  width  of 
the  pole-face.  The  relations  would  be 
as  shown  in  Fig.  40.  He  regarded  this 
result  as  in  a  measure  growing  out  of  the 
condition  of  displacement  of  lines,  indr 
cated  in  Fig.  41,  where  the  current  in 
the  armature -coil  drew  the  lines  together, 
leaving  the  field,  or  bunched  them 


195 


through  its  own  center  in  the  position 
indicated.  In  dealing  with  the  heating 
of  armature  conductors  by  eddy-currents, 
the  author  had  drawn  a  distinction  be- 
tween coils  with  and  without  iron  cores, 
showing  the  need  of  an  explanation  of 
the  differences  noted.  His  own  view  of 
the  matter  had  for  some  time  been  this : 
It  is  well  known  that,  in  a  transformer 
with  a  well-closed  iron  circuit,  very  large 
sections  of  conductors  might  be  employed 


Fig.  40 


Fig.  41 


in  the  coils  without  introducing  trouble 
from  eddy-currents.  The  extreme  case 
occurred  in  transformers  for  electric 
welding,  in  which  the  section  of  the 
single  secondary  turn  might  be  many 
square  inches  without  showing  the  effects 
of  eddy-currents.  The  reason,  as  it 
appeared  to  him,  for  such  a  condition 


196 

was  that  the  development  of  lines,  taking 
place  as  circular  magnetism  around  the 
primary  conductors,  was  carried  out  with 
great  speed  to  the  lodgment  of  the  lines 
in  the  iron  shell  or  core.  Thus  all  parts 
of  the  secondary  conductor  were  cut  at 
almost  the  same  instant,  by  each  line 
evolved,  in  its  passage  to  the  iron  core, 
the  same  actions  being  repeated  at  each 
alternation.  The  great  speed  at  which 
the  lines  passed  the  conductor  in  such 
cases,  in  going  to  the  iron  core,  left  no 
time  during  which  differences  of  electro- 
motive force  in  parts  of  the  conductor 
might  act  to  induce  eddy-currents.  Now, 
when  a  coil  without  an  iron  core  passed 
through  a  field,  the  speed  of  cutting  did 
not  exceed  the  speed  of  motion,  so  that 
if  the  lines  being  cut  by  a  conductor 
were  denser  at  one  point  than  at  another, 
eddy- currents  resulted.  Provide  the 
coil  with  an  iron  core  and  the  lines  re- 
main in  the  core  until  dragged  out,  as  it 
were,  by  the  movement  given  to  it  in 
front  of  the  field-cores,  at  which  time  the 
lines  move  through  the  space  between 


197 

the   successive  cores  with    great   speed, 
and  cut  all  parts  of  the  conductor  at  the 


same  instant.     The  lines  snap  out  of  the 
leaving  core,  as  it  were,  and  pass  quickly 


198 

to  the  incoming  core,  producing  a  \veak 
field  between  the  two  composed  of  few 
lines  moving  at  great  speeds.  Figs.  42 
and  43  represented  the  two  conditions 
comparatively.  Fig.  42  showed  a  coil 
without  core  cutting  lines  between  N  and 
S ;  and  Fig.  43  the  progressive  move- 
ment of  coils  with  iron  cores  through 
the  field.  The  rapid  movement  of  the 
lines  backward  across  the  space  between 
the  iron  armature-cores,  or  projections, 
II,  Fig.  43,  as  the  armature  moved  for- 
ward, pointed  also  to  the  necessity  for 
laminatioi}  of  the  field-poles  when  such 
cores  or  projections  were  used.  The 
turns  of  armature-conductor  nearest  the 
enclosed  iron  core  would  be  subject  to 
eddy-currents,  on  account  of  the  field 
density  being  made  more  irregular  by 
the  bending  of  the  lines  leaving  the  iron. 
He  was  of  opinion  that  the  use  of  "  horns  '' 
on  pole-pieces  was  not  akin  to  the  effects 
just  mentioned,  excepting  in  so  far  as  the 
entering  and  leaving  field  was  more 
spread  out  or  graduated  in  density,  and 
so  placed  the  parts  of  a  large  section 


199 

armature- conductor  in  substantially  equal 
field  densities  at  any  instant  during 
movement  into  or  out  of  the  field.  This 
was  not  the  case  where  no  horns  were 
used,  or  where  the  field  was  abrupt  and 
permitted,  say,  one-half  the  section  of 
the  armature-conductor  to  be  at  any  in- 
stant cutting  dense  lines,  and  the  other 
half  to  be  moving  in  a  field  of  little  density. 
Making  the  conductor  of  insulated  strands, 
and  twisting  the  strands,  was  the  remedy 
indicated. 


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AXON  (W.  E.  A.)  The  Mechanic's  Friend  :  a  Collection  of  Re- 
ceipts and  Practical  Suggestions  Relating  to  Aquaria — 
Bronzing— Cements— Drawing— Dyes— Electricity— Gilding 
— Glass-working  —  Glues  —  Horology  —  Lacquers  —Locomo- 
tives—Magnetism— Metal-working  -  Modelling  —  Photogra- 
phy— Pyrotechny — Railways — Solders — Steam-Engine — Tel- 
egraphy— Taxidermy — Varnishes — Waterproofing,  and  Mis- 
cellaneous Tools,  Instruments,  Machines,  and  Processes 
connected  with  the  Chemical  and  Mechanic  Arts.  With  nu- 
merous diagrams  and  wood-cuts.  Fancy  cloth  ..150 

BACON  (F.  W.)  A  Treatise  on  the  Richards  Steam-Engine 
Indicator,  with  directions  for  its  use.  By  Charles  T.  Por- 
ter. Revised,  with  notes  and  large  additions  as  developed 
by  American  practice ;  with  an  appendix  containing  useful 
formulae  and  rules  for  engineers.  Illustrated.  Third  edi- 
tion. i2mo,  cloth i  oo 


2  D.    VAN   NOSTRAND  S   PUBLICATIONS. 

BARBA  (J.)  The  Use  of  Steel  for  Constructive  Purposes  ; 
Method  of  Working,  Applying,  and  Testing  Plates  and 
Brass.  With  a  Preface  by  A.  L.  Holley,  C.E.  12010,  cloth.fti  50 

BARNES  (Lt.  Com.  J.  S.,  U.  S."  N.)  Submarine  Warfare,  offen- 
sive and  defensive,  including  a  discussioa  of  the  offensive 
Torpedo  System,  its  effects  upon  Iron-Clad  Ship  Systems 
and  influence  upon  future  naval  wars.  With  twenty  litho- 
graphic plates  and  many  wood-cuts.  8vo,  cloth  ............  5  oo 

BEILSTEIN  (F.)     An  Introduction  to  Qualitative  Chemical 

Analysis,  translated  by  I.  J.  Osbun.    i2mo,  cloth  ..........      75 

BENET  (Gen.  S.  V.,  U.  S.  A.)  Electro-Ballistic  Machines,  and 
the  Schultz  Chronoscope.  Illustrated.  Second  edition,  410, 
cloth  ......................................................  3  oo 

BLAKE  (W.  P.)  Report  upon  the  Precious  Metals  ;  Being  Sta- 
tistical Notices  of  the  principal  Gold  and  Silver  producing 
regions  of  the  World,  represented  at  the  Paris  Universal 
Exposition.  8vo,  cloth  .....................................  2  oo 

-  Ceramic  Art.  A  Report  on  Pottery,  Porcelain,  Tiles, 

Terra  Cotta,  and  Brick.  8vo,  cloth  ........................  200 

BOW  (R.  H.)  A  Treatise  on  Bracing,  with  its  application  to 
Bridges  and  other  Structures  of  Wood  or  Iron.  156  illustra- 
tions. 8vo,  cloth  .....  ...............  „  ....................  i  50 


BOWSER  (Prof.   E.  A.)    An  Elementary  Treatise  on  Analytic 
Geometry,  embracing  Plane  Geometry,  and  an  Introduc- 
tion to  Geometry  of  three  Dimensions.    i2mo,  cloth  .......  i  75 

An  Elementary  Treatise  on  the  Differential  and  Integral 


Calculus.    With  numerous  examples.    i2mo,  cloth  .........  225 

BURGH  (N,  P.)  Modern  Marine  Engineering,  applied  to  Pad- 
dle and  Screw  Propulsion.  Consisting  of  36  colored  plates, 
259  practical  wood-cut  illustrations,  and  403  pages  of  de- 


, 

scriptive  matter,  the  whole  being  an  exposition  of  the  pre- 
sent practice  of  Tames  Watt  &  Co.,  J.  &  G.  Rennie,  R.  Na- 
pier &  Sons,  and  other  celebrated  firms.  Thick  410  vol., 


,  .  . 

cloth  ..............  .....................................  10  oo 

Half  morocco  ..............................................  15  oo 

BUR  T  (W.  A.)  Key  to  the  Solar  Compass,  and  Surveyor's  Com- 
panion ;  comprising  all  the  rules  necessary  for  use  in  the 
field:  also  description  of  the  Linear  Surveys  and  Public 
Land  Astern  of  the  United  States,  Notes  on  the  Barome- 
ter, •.t.gestions  for  an  outfit  for  a  survey  of  four  months, 
etc.  Second  edition.  Pocket-book  form,  tuck  .............  250 

BUTLER  (Capt.  J.  S.,  U.  S.  A.)  Projectiles  and  Rifled  Cannon. 
A  Critical  Discussion  of  the  Principal  Systems  of  Rifling 
and  Projectiles,  with  Practical  Suggestions  for  their  Im- 
provement, as  embraced  in  a  Report  to  the  Chief  of  Ord- 
nance, U.  S.  A.  36  plates  410,  cloth  .......................  6  00 


D.    VAN    NOSTRAXD  S   PUBLICATIONS.  3 

CAIN  (Prof.  WM  )     A  Practical  Treatise  on  Voussoir  and  Solid 

and  Braced  Arches.    i6mo,  cloth  extra. $i  75 

CALDWELL  (Prof.  GEO.  C.)  and  BRENEM  AN  (Prof.  A.  A.) 
Manual  of  Introductory  Chemical  Practice,  for  the  use  of 
Students  in  Colleges  and  Normal  and  High  Schools.  Third 
edition,  revised  and  corrected.  8vo,  cloth,  illustrated.  New 
and  enlarged  edition. I  50 

CAMPIN  (FRANCIS).    Onthe  Construction  oflron  Roofs.  8vo, 

wit  h  plates,  cloth 2  oo 

CHAUVENET  (Prof.  W.)  New  method  of  correcting  Lunar 
Distances,  and  improved  method  of  finding  the  error  and 
rate  of  a  chronometer,  by  equal  altitudes.  8vo,  cloth 2  oo 

CHURCH  (JOHN  A.)     Notes  of  a  Metallurgical  Journey  in 

Europe.     8vo,  cloth 200 

CLARK  (D.  KINNEAR,  C.E.)  Fuel:  Its  Combustion  and 
Economy,  consisting  of  Abridgments  of  Treatise  on  the 
Combustion  of  Coal  and  the  Prevention  of  Smoke,  by  C. 
W.  Williams ;  and  the  Economy  of  Fuel,  by  T  S  Pri- 
deaux.  With  extensive  additions  on  recent  practice  in  the 
Combustion  and  Economy  of  Fuel :  Coal,  Coke,  Wood, 
Peat,  Petroleum,  etc.  i2mo,  cloth I  50 

— A  Manual  of  Rules,  Tables,  and  Data  for  Mechanical 

Engineers.  Based  on  the  most  recent  investigations.     Illus- 
trated with  numerous  diagrams.     1,012  pages.    8vo,  cloth...  7  50 
Half  morocco 10  oo 

CLARK  (Lt.  LEWIS,  U.  S.  N  )  Theoretical  Navigation  and 
Nautical  Astronomy.  Illustrated  with  41  wood-cuts.  8vo, 
cloth I  50 

CLARKE  (T.  C)  Description  of  the  Iron  Railway  Bridge  over 
the  Mississippi  River  at  Quincy,  Illinois.  Illustrated  with 
21  lithographed  plans.  410,  cloth 7  50 

CLEVENGER  (S.  R.)  A  Treatise  on  the  Method  of  Govern- 
ment Surve\ing,  as  prescribed  by  the  U.  S.  Congress  and 
Commissioner  of  the  General  Land  Office,  with  complete 
Mathematical,  Astronomical,  and  Practical  Instructions  for 
the  use  of  the  United  States  Surveyors  in  the  field.  i6mo, 
morocco  2  y> 

COFFIN  (Prof  J.  H.  C.)  Navigation  and  Nautical  Astrono- 
my. Prepared  for  the  use  of  the  U.  S.  Naval  Academy. 
Sixth  edition.  52  wood-cut  illustrations.  I2mo,  cloth 3  50 

COLBURN   (ZERAH).    The  Gas-Works  of  London.     i2mo, 

boards 60 

COLLINS  (JAS.  E.)    The  Private  Book  of  Useful  Alloys  and 

Memoranda  for  Goldsmiths,  Jewellers,  etc.     i8mo,  cloth. ..      50 


4  D.    VAN   NOSTRAND  S   PUBLICATIONS. 

CORNWALL  (Prof.  H.  B.)  Manual  of  Blow  Pipe  Analysis, 
Qualitative  and  Quantitative,  with  a  Complete  System  of 
Descriptive  Mineralogy.  8vo,  cloth,  with  many  illustra- 
tions. N.  Y.,  1882 $250 

CRAIG  (B.  F)  Weights  and  Measures.  An  account  of  the 
Decimal  System,  with  Tables  of  Conversion  for  Commer- 
cial and  Scientific  Uses.  Square  32010,  limp  cloth 50 

CRAIG  (Prof.  THOS.)    Elements  of  the  Mathematical  Theory 

of  Fluid  Motion.     i6mo,  cloth 125 

DAVIS  (C.  B.)  and  RAE  (F.  B.)  Hand-Book  of  Electrical  Dia- 
grams and  Connections.  Illustrated  with  32  full-page  illus- 
trations. Second  edition.  Oblong  8vo,  cloth  extra  2  oo 

D1EDRICH  (JOHN).  The  Theory  of  Strains  :  a  Compendium 
tor  the  Calculation  and  Construction  of  Bridges,  Roofs,  and 
Cranes.  Illustrated  by  numerous  plates  and  diagrams. 
8vo,  cloth 5  oo 

DIXON  (D.  B.)  The  Machinist's  and  Steam-Engineer's  Prac- 
tical Calculator.  A  Compilation  of  useful  Rules,  and  Prob- 
lems Arithmetically  Solved,  together  with  General  Informa- 
tion applicable  to  Shop-Tools,  Mill-Gearing,  Pulleys  and 
Shafts,  Steam-Boilers  and  Engines.  Embracing  Valuable 
Tables,  and  Instruction  in  Screw-cutting,  Valve  and  Link 
Motion,  etc.  i6mo,  full  morocco,  pocket  form  .  ..(In  press) 

DODD  (GEO.)  Dictionary  of  Manufactures,  Mining,  Ma- 
chinery, and  the  Industrial  Arts.  I2mo,  cloth I  50 

DOUGLASS  (Prof  S.  H.)  and  PRE3COTT  (Prof.  A.  B.)  Qual- 
itative Chemical  Analysis.  A  Guide  in  the  Practical  Study 
of  Chemistry,  and  in  the  Work  of  Analysis.  Third  edition. 
8vo,  cloth 3  50 

DUBOIS  (A.  J.)   The  New  Method  of  Graphical  Statics.  With 

60  illustrations.    8vo,  cloth i  50 

EASSIE  (P.  B.)  Wood  and  its  Uses.  A  Hand-Book  for  the  use 
of  Contractors,  Builders,  Architects,  Engineers,  and  Tim- 
ber Merchants.  Upwards  of  250  illustrations.  8vo,  cloth,  i  50 

EDDY  (Prof.  H.  T.)  Researches  in  Graphical  Statics,  errbiac- 
ing  New  Constructions  in  Graphical  Statics,  a  New  General 
Method  in  Graphical  Statics,  and  the  Theory  of  Internal 
Stress  in  Graphical  Statics.  8vo,  cloth ^ i  c>o 

ELIOT  (Prof.  C.  W.)  and  STORER  (Prof.  F.  H.)  A  Compen- 
dious Manual  of  Qualitative  Chemical  Analysis.  Revised 
with  the  co-operation  of  the  authors.  By  Prof.  William  R. 
Nichols.  Illustrated.  i2mo,  cloth i  50 

ELLIOT  (Maj.  GEO.  H.,  U.  S.  R.)  European  Light-House 
Systems.  Being  a  Report  of  a  Tour  of  Inspection  made  in 
1873.  51  engravings  and  21  wood-cuts.  8vo,  cloth 5  oo 


D.    VAN  NOSTRAND  S  PUBLICATIONS.  O 

ENGINEERING  FACTS  AND  FIGURES.  An  Annual 
Register  of  Progress  in  Mechanical  Engineering  and  Con- 
struction for  the  years  1863-6.1-65-66-67-68.  Fully  illus- 
trated. 6  vols.  i8mo,  cloth  (each  volume  sold  separatel>), 
per  vol $2  50 

FANNING  (J.  T.)  A  Practical  Treatise  of  Water-Supply  En- 
gineering. Relating  to  the  Hydrology,  Hydro  dynamics,  and 
Practical  Construction  oi  Water-Works  in  North  America. 
Third  edition.  With  numerous  tables  and  180  illustra- 
tions, 65opages.  8vo,  cloth 500 

FISkE  (BRADLEY  A.,  U.S.  N.)    Electricity  in  Theory  and 

Practice.    8vo,  cloth 2  «;o 

FOSTER  (Gen.  J.  G.,  U.  S.  A.)  Submarine  Blasting  in  Boston 
Harbor,  Massachusetts.  Removal  ot  Tower  and  Ccrwin 
Rocks.  Illustrated  with  seven  plates.  410,  cloth 3  50 

FOYE  (Prof.  J.  C.)  Chemical  Problems.  With  brief  State- 
ments of  the  Principles  involved.  Second  edition,  revised 
and  enlarged.  i6mo,  boards 50 

FRANCIS  (JAS.  B.,  C  E.)  Lowell  Hydraulic  Experiments : 
Being  a  selection  from  Experiments  on  Hydraulic  Motors, 
on  the  Flow  of  Water  over  Weirs,  in  Open  Canals  of  Uni- 
form Rectangular  Section,  and  through  submerged  Orifices 
and  diverging  Tubes.  Made  at  Lowell,  Massachusetts. 
Fourth  edition,  revised  and  enlarged,  with  many  new  ex- 
periments, and  illustrated  with  twenty-three  copperplate 
engravings.  410,  cloth , 15  oo 

FREE-HAND  DRAWING.  A  Guide  to  Ornamental  Figure 
and  Landscape  Drawing.  By  an  Art  Studen,.  i8mo, 
boards 50 

GILLMORE  (Gen.  Q.  A.)  Treatise  on  Limes,  Hydraulic  Ce- 
ments, and  Mortars.  Papers  on  Practical  Engineering,  U. 
S.  Engineer  Department,  No.  9,  containing  Reports  or 
numerous  Experiments  conducced  in  New  York  City  during 
the  years  1858  to  1861,  inclusive.  With  numerous  illustra- 
tions. 8vo,  cloth 40O 

Practical  Treatise  on  the  Construction  of  Roads,  Streets, 

and  Pavements.     With  70  illustrations.     I2mo,  cloth 2  oo 


Report  on  Strength  of  the  Building  Stones  in  the  United 

States,  etc.    8vo,  illustrated,  cloth    .    150 

Coignet  Beton  and  other  Artificial  Stone.    9  plates,  views, 

etc.    8vo,  cloth 2  50 

GOODEVE  (T.  M.)    A  Text-Book  on  the  Steam-Engine.     143 

illustrations.     I2mo,  cloth ?  oo 

GORDON  (J.  E.  H.)   Four  Lectures  on  Static  Induction.    lamo, 

cloth 80 


6  D.  VAN  NOSTRAND'S  PUBLICATIONS. 

GRUNER  (M.  L.)  The  Manufacture  of  Steel.  Translated 
from  the  French,  by  Lenox  Smith,  with  an  appendix  on  the 
Bessemer  process  in  the  United  States,  by  the  translator. 
Illustrated.  8vo,  cloth $3  50 

HALF-HOURS  WITH  MODERN  SCIENTISTS.  Lectures 
and  Essays.  By  Professors  Huxley,  Barker,  Stirling,  Cope, 
Tyndall,  Wallace,  Rpscoe,  Hoggins,  Lockyer,  Young, 
Mayer,  and  Reed.  Being  the  University  Series  bound  up. 
With  a  general  introduction  by  Noah  Porter,  President  of 
Yale  College.  2  vols  12010,  cloth,  illustrated 2  50 

HAMILTON  (W.  G.)  Useful  Information  for  Railway  Men. 
Sixth  edition,  revised  and  enlarged  562  pages,  pocket  form. 
Morocco,  gilt 200 

HARRISON  (W.  B.)  The  Mechanic's  Tool  Book,  with  Prac- 
tical Rules  and  Suggestions  for  Use  of  Machinists,  Iron- 
Workers,  and  others.  Illustrated  with  44  engravings. 
I2mo,  cloth i  50 

HASKINS  (C.  H.)  The  Galvanometer  and  its  Uses.  A  Man- 
ual  for  Electricians  and  Students.  Second  edition.  I2mo, 
morocco . .  i  50 

HENRICI  (OLAUS).  Skeleton  Structures,  especially  in  their 
application  to  the  Buildingof  Steel  and  Iron  Bridges.  With 
folding  plates  and  diagrams.  8vo,  cloth I  50 

HEWSON  (WM.)  Principles  and  Practice  of  Embanking 
Lands  from  River  Floods,  as  applied  to  the  Levees  of  the 
Mississippi.  8vo,  cloth 2  oo 

HOLLEY  (ALEX.  L.)  A  Treatiseon  Ordnance  and  Armor,  em- 
bracing descriptions,  discussions,  and  professional  opinions 
concerning  the  materials,  fabrication,  requirements,  capa- 
bilities, and  endurance  of  European  and  American  Guns, 
for  Naval,  Sea-Coast,  and  Iron-Clad  Warfare,  and  their 
Rifling,  Projectiles,  and  Breech-Loading;  also,  results  of 
experiments  against  armor,  from  official  records,  with  an 
appendix  referring  to  Gun-Cotton,  Hooped  Guns,  etc.,  etc. 
948  pages,  493  engravings,  and  147  Tables  of  Results,  etc. 
8vo,  half  roan 10  oo 

Railway  Practice  American  and  European  Railway 

Practice  in  the  economical  Generation  of  Steam,  including 
the  Materials  and  Construction  of  Coal-burning  Boilers, 
Combustion,  the  "Variable  Blast,  Vaporization,  Circulation, 
Superheating,  Supplying  and  Heating  Feed-water,  etc., 
and  the  Adaptation  of  Wood  and  Coke-burning  Engines  to 
Coal-burning;  and  in  Permanent  Way,  including  Road-bed, 
Sleepers,  Rails,  Joint-fastenings,  Street  Railways,  etc.,  etc. 
With  77  lithographed  plates.  Folio,  cloth 12  «o 

HOWARD  (C.  R.)  Earthwork  Mensuration'  on  the  Basis  of 
the  Prismoidal  Formulae.  Containing  simple  and  labor- 
saving  method  of  obtaining  Prismoidal  Contents  directly 


D.    VAN   NOSTRAND  S    PUBLICATIONS.  7 

from  End  Areas.  Illustrated  by  Examples,  and  accom- 
panied by  Plain  Rules  for  Practical  Uses.  Illustrated.  8vo, 
cloth  $l  50 

INDUCTION-COILS.  How  Made  and  How  Used.  63  illus- 
trations. i6mo,  boards  „ 50 

ISHERWOOD  (B.  F.)  Engineering  Precedents  for  Steam  Ma- 
chinery. Arranged  in  the  most  practical  and  useful  manner 
for  Engineers.  With  illustrations.  Two  volumes  in  one. 
8vo,  cloLh 250 

JANNETTAZ  (EDWARD).  A  Guide  to  the  Determination  of 
Rocks:  being  an  Introduction  to  Lithology.  Translated 
from  the  French  by  G.  W.  Plympton,  Professor  of  Physical 
Science  at  Brooklyn  Polytechnic  Institute.  I2mo,  cloth i  50 

JEFFERS  (Capt.  W.  N.,  U.  S.  N.)  Nautical  Surveying.  Illus- 
trated with  9  copperplates  and  31  wood-cut  illustrations. 
8vo,  cloth 5  oo 

JONES  (H.  CHAPMAN).  Text-Book  of  Experimental  Or- 
ganic Chemistry  for  Students.  i8mo,  cloth I  oo 

JOYNSON  (F.  H.)  The  Metals  used  in  Construction:  Iron, 

Steel,  Bessemer  Metal,  etc.,  etc.  Illustrated.  i2mo,  cloth.  75 

Designing  and  Construction  of  Machine  Gearing.  Illus- 
trated 8vo,  cloth , , 2  oo 

KANSAS  CITY  BRIDGE  (THE).  With  an  account  of  the 
Regimen  of  the  Missouri  River,  and  a  description  of  the 
methods  used  for  Founding  in  that  River.  By  O.  Chanute, 
Chief-Engineer,  and  George  Morrison,  Assistant-Engineer, 
fllustrated  with  five  lithographic  views  and  twelve  plates  of 
plans.  4to,cloth... 600 

KING  (W.  H.)  Lessons  and  Practical  Notes  on  Steam,  the 
Steam-Engine,  Propellers,  etc.,  etc,  for  young  Marine  En- 
gineers, Students,  and  others.  Revised  "by  Chief-Engineer 
J.  W.  King,  U.  S.  Navy.  Nineteenth  edition,  enlarged. 
8vo,  cloth 2  oo 

KIRKWOOD  (JAS.  P.)  Report  on  the  Filtration  of  River 
Waters  for  the  supply  of  Cities,  as  practised  in  Europe, 
made  to  the  Board  of  Water  Commissioners  of  the  City  of 
St.  Louis.  Illustrated  by  30  double-plate  engravings.  410, 
cloth 1500 

LARRABEE  (C.  S.)  Cipher  and  Secret  Letter  and  Telegra- 
phic Code,  with  Hogg's  Improvements.  The  most  perfect 
secret  code  ever  invented  or  discovered.  Impossible  to  read 
without  the  key.  i8mo,  cloth I  oo 

LOCK  (C.  G.),  WIGNER  (G.  W.),  and  HARLAND  (R.  H.) 
Sugar  Growing  and  Refining.  Treatise  on  the  Culture  of 
Sugar-Yielding  Plants,  and  the  Manufacture  and  Refining  of 
Cane,  Beet,  and  other  sugars.  8vo,  cloth,  illustrated 12  oo 


D.  VAN  NOSTRAND'S  PUBLICATIONS. 

LOCKWOOD  (THOS.  D.)  Electricity,  Magnetism,  and  Elec- 
tro-Telegraphy. A  Practical  Guide  for  Students,  Operators, 
and  Inspectors.  8vo,  cloth  ....................  .......  g2  e;o 

LORING  (A.  E.)    A  Hand-Book  on  the  Electro-Magnetic  Tele- 

graph.    Paper  boards  .....................................         50 

Cloth  ..................  ;  .............................  .....        75 

Morocco  ...................................................   I  oo 

MACCORD  (Prof.  C.  W  )  A  Practical  Treatise  on  the  Slide. 
Valve  by  Eccentrics,  examining  by  methods  the  action  of 
the  Eccentric  upon  the  Slide-Valve,  and  explaining  the  prac- 
tical processes  of  laying  out  the  movements,  adapting:  th» 
valve  for  its  various  duties  in  the  steam-engine.  Second  edi- 
tion Illustrated.  4to,  cloth  ..............................  250 

McCULLOCH  (Prof.  R  S.)  Elementary  Treatise  on  the  Me- 
chanical Theory  of  Heat,  and  its  application  to  Air  and 
Steam  Engines.  8vo,  cloth  .................................  3  50 

MERRILL  (Col.  WM.  E  ,  U.  S.  A.)  Iron  Truss  Bridges  for 
Railroads.  The  method  of  calculating  strains  in  Trusses, 
with  a  careful  comparison  of  the  most  prominent  Trusses,  in 
reference  to  economy  in  combination,  etc.,  etc.  Illustrated. 
4to,  cloth  ...........  ...................................  500 

MICHAELIS  (Capt.  O.  E.,  U.  S.  A.)  The  Le  Boulenge 
Chronograph,  with  three  lithograph  folding  plates  of  illus- 
trations. 410,  cloth  .......................................  300 


MICHIE  (Prof.  P.  S.)  Elements  ot  Wave  Motion  relating  to 
Sound  and  Light.  Text-Book  forthe  U.S.  Military  Acade- 
my. 8vo,  cloth,  illustrated  .................................  5  oo 


MINIFIE  (WM.)  Mechanical  Drawing.  A  Text-Book  of  Geo- 
metrical Drawing  for  the  use  of  Mechanics  and  Schools,  in 
which  the  Definitions  and  Rules  of  Geometry  are  familiarly 
explained ;  the  Practical  Problems  are  arranged,  from  the 
most  simple  to  the  more  complex,  and  in  their  description 
technicalities  are  avoided  as  much  as  possible.  With  illus- 
trations for  Drawing;  Plans,  Sections,  and  Elevations  of 
Railways  and  Machinery;  an  Introduction  to  Isometrical 
Drawing,  and  an  Essayon  Linear  Perspective  and  Shadows. 
Illustrated  with  over  200 diagrams  engraved  on  steel.  Ninth 
edition.  With  an  Appendix  on  the  Theory  and  Application 

of  Colors.    8vo,  cloth  4  oo 

"It  is  the  best  work  on  Drawing  that  we  have  ever  seen,  and  is 
especially  a  text -book  of  Geometrical  Drawing  for  the  use  of  Me- 
chanics and  Schools.  No  young;  Mechanic,  such  as  a  Machinist, 
Engineer,  Cabinet-maker,  Millwright,  or  Carpenter,  should  be  with- 
out it."— Scientific  American. 

••  Geometrical  Drawing.  Abridged  from  the  octavo  edi- 
tion, for  the  use  of  schools.  Illustraced  with  forty-eight 
steel  plates.  Fifth  edition.  i2mo,  cloth  200 


D.  VAX  NOSTBAND'S  PUBLICATIONS.  9 

MODERN  METEOROLOGY.  A  Series  of  Six  Lectures,  de- 
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101878.  Illustrated.  I2mo,  cloth $150 

MORRIS  (E.)  Easy  Rules  for  the  Measurement  of  Earth- 
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MOTT  (H.  A  ,  Jr.)  A  Practical  Treatise  on  Chemistry  (Quali- 
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Analysis,  Mineralogy,  Assaying,  Pharmaceutical^  Prepara- 
tions, Human  Secretions,  Specific  Gravities,  Weights  and 
Measures,  etc.,  etc.,  etc.  New  edition,  1883.  650  pages. 
8vo,  cloth 4  00 

NAQUET  (A  )  Legal  Chemistry.  A  Guide  to  the  Detection  of 
Poisons,  Falsification  of  Writings,  Adulteration  of  Alimen- 
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and  examination  of  Hair,  Coins,  Arms,  and  Stains,  as  ap» 
plied  to  Chemical  Jurisprudence,  for  the  use  of  Chemists, 
Physicians,  Lawyers,  Pharmacists,  and  Experts.  Translat- 
ed, with  additions,  including  a  list  of  books  and  Memoirs  on 
Toxicology,  etc.,  from  the  French.  By  J.  P.  Battershall, 
Ph.D.,  with  a  preface  by  C.  F.  Chandler,  Ph.D.,  M.D., 
LL.D.  i2mo,  cloth 200 

NOBLE  (W.H.)    Useful  Tables.    Pocket  form,  cloth 90 

NUGENT  (E.)  Treatise  on  Optics ;  or,  Light  and  Sight,  theo- 
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I2mo,  cloth I  50 

PEIRCE  (B.)    System  of  Analytic  Mechanics.    4to,  cloth lo  OO 

PLANE  \BLE  'THE).  Its  Uses  in  Topographical  Survey 
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"  This  work  gives  a  description  of  the  Plane  Table  employed  at 

the  U.  S.  Coast  Survey  office,  and  the  manner  of  using  it." 

PLATTNER.  Manual  of  Qualitative  and  Quantitative  An- 
alysis with  the  Blow-Pipe.  From  the  last  German  edition, 
revised  and  enlarged.  By  Prof.  Th.  Richter,  of  the  Royal 
Saxon  Mining  Academy.  Translated  by  Prof.  H.  B.  Corn- 
wall, assisted  by  John  H.  Caswell.  Illustrated  with  87  wood- 
cuts arid  one  lithographic  plate.  Fourth  edition,  revised, 
560  pages.  8vo,  cloth 5  oo 

MLYMPTON  (Prof.  GEO.  W.)  The  Blow-Pine.  A  Guide  to  its 
use  in  the  Determination  of  Salts  and  Minerals.  Compiled 

from  various  sources.     I2mo,  cloth. I  50 

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10    ffi    D.  VAN  NOSTRAND'S  PUBLICATIONS. 

PLYMPTON  (Prof.  GEO.  W.)  The  Star-Finder,  or  Plani- 
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card-board,  and  in  accordance  with  Proctor's  Star  Atlas. .  .j$i  oo 

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ing Logarithms  of  Numbers,   and  Logarithmic  Sines  and 
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Natural  Sines,  Tangents,  and  Co-Tangents.      i6mo,  boards,      C.Q 
Morocco .  i  oo 

POOK  (S.  M.)  Method  of  Comparing  the  Lines  and  Draught- 
ing Vessels  propelled  by  Sail  or  Steam.  Including  a  chap- 
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illustrations,  cloth c  oo 

POPE  (F.  L.)  Modern  Practice  of  the  Electric  Telegraph.  A 
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PRESCOTT  (Prof.  A.  B  )  Outlines  of  Proximate  Organic  An- 
alysis, for  the  Identification,  Separation,  and  Quantitative 
Determination  of  the  more  commonly  occurring  Organic 
Compounds.  i2mo,  cloth *. i  « 

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tive Determinations.  I2mo,  cloth 150 

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PYNCHON  (Prof.  T.  R.)  Introduction  to  Chemical  Physics, 
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Schools.  Illustrated  with  numerous  engravings,  and  con- 
taining copious  experiments  with  directions  for  preparing 
them.  New  edition,  revised  and  enlarged,  and  illustrated 
by  269  illustrations  on  wood.  Crown  8vo,  cloth 3  oo 

RAMMELSBERG  (C.  F.)  Guide  to  a  Course  of  Quantitative 
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ducts. Illustrated  by  Examples.  Translated  by  J.  Towler, 
M.D.  8vo,  cloth '  2  25 

RANDALL  (P.  M.)  Quartz  Operat9r's  Hand-Book.  New  edi- 
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RANKINE  (W.  J.  M.)  _  Applied  Mechanics,  comprising  Prin- 
ciples of  Statics,  Cinematics,  and  Dynamics,  and  Theory 
ot  Structures,  Mechanism,  and  Machines.  Crown  8vo, 

cloth.    Tenth  edition.    London 500 

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with  numerous  tables  and  illustrations.  Crown  8vo,  cloth. 
Tenth  edition.  London,  1882 5  oo 

— A  Selection  from  the  Miscellaneous  Scientific  Papers  of, 

with  Memoir  by  P.  G.  Tait,  and  edited  by  W.  J.  Millar,  C.E. 
8vo,  cloth.    London,  1880 .10  oo 


D.  VAN  NOSTRAND'S  PUBLICATIONS.          11 

RANKINE  (W.  J.  M.)  A  Manual  of  Machinery  and  Mill-work. 

Fourth  edition.    Crown  8vo.    London,  1881     $500 

Civil    Engineering,    comprising    Engineering    Surveys, 

Earthwork,    Foundations,     Masonry,     Carpentry,     Metal- 
works,    Roads,    Railways,    Canals,    Rivers,    Water-works, 
Harbors,    etc.,    with     numerous     tables  and   illustrations. 
Fourteenth  edition,  revised  by  E.  F.  Bamber,  C.E.      8vo. 
London,  1883 6  50 

Useful  Rules  and  Tables  for  Architects,  Builders,  Car- 
penters,  Coachbuilders,     Engineers,     Founders,    Mechan- 
ics, Shipbuilders,  Surveyors,   Typefounders,  Wheelwrights, 

etc.     Sixth  edition.     Crown  8vo,  cloth.     London,  1883 4  oo 

and  BAMBER  (E.  F.)    A   Mechanical  Text-Book ;  or, 

Introduction  to  the  Study  of  Mechanics  and  Engineering. 
8vo,  cl -th.     London,    1875  3  SO 

RICE  (Prof.  J.  M.)  and  JOHNSON  (Prof.  W.  W.)  On  a  New 
Method  of  Obtaining  the  Differentials  of  Functions,  with 
especial  reference  to  the  Newtonian  Conception  of  Rates  or 
Velocities.  i2mo,  paper  50 


isays 

sils,  and  a  description  of  the  Coal  Fields  of  North  America 
and  Great  Britain.  Illustrated  with  Plates  and  Engravings 
in  the  text.  3  vols.  410,  cloth,  with  Portfolio  of  Maps 30  oo 

ROEBLING  (J.  A)  Long  and  Short  Span  Railway  Bridges. 
Illustrated  with  large  copperplate  engravings  cf  plans  and 
views.  Imperial  folio,  cloth 25  oo 

ROSE  (IOSHUA,  M.E.)  The  Pattern-Maker's  Assistant,  em- 
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and  Practical  Gear  Constructions,  the  Preparation  and  Use 
of  Tools,  together  with  a  large  collection  of  useful  and  val- 
uable Tables.  Third  edition.  Illustrated  with  250  engrav- 
ings. 8vo,  cloth 2  50 

SABINE  (ROBERT).  History  and  Progress  of  the  Electric  Tel- 
egraph, with  descriptions  of  some  of  the  apparatus.  Second 
edition,  with  additions,  i2mo,  cloth I  25 

SA£LTZER(ALEX  }    Treatise  on  Acoustics  in  connection  with 

Ventilation.     I2mo,  cloth I  oo 

SCHUMANN  (F)  A  Manual  of  Heating  and  Ventilation  in 
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sions of  heating,  flow  and  return  pipes  for  steam  and  hot- 
water  boilers,  flues,  etc.,  etc.  I2mo.  Illustrated.  Full 
roan  ... i  50 

Formulas  and  Tables  for  Architects  and   Engineers  in 

calculating  the  strains  and  capacity  of  structures  in  Iron 
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12          D.  VAN  NOSTRAND'S  PUBLICATIONS. 

SAWYER  (W.  E.)  Electric-Lighting  by  Incandescence,  and 
its  Application  to  Interior  Illumination.  A  Practical 
Treatise.  With  96  illustrations.  Third  edition.  8vo,  cloth. $2  50 

SCRIBNER  (J.  M.)    Engineers'  and  Mechanics' Companion, 


cles,  the  Mechanical  Powers,  Centres  of  Gravity,  Gravita- 
tion of  Bodies,  Pendulums,  Specific  Gravity  or  Bodies, 
Strength,  Weight,  and  Crush  of  Materials,  Water-Wheels, 
Hydrostatics,  Hydraulics,  Statics,  Centres  of  Percussion 
and  Gyration,  Friction  Heat,  Tables  of  the  Weight  of 
Metals,  Scantling,  etc.,  Steam  and  the  Steam-Engine. 
Nineteenth  edition,  revised,  i6mo,  full  morocco I  50 

---  Engineers',  Contractors',  and  Surveyors'  Pocket  Table- 
Book.  Comprising  Logarithms  of  Numbers,  Logarithmic 
Sines  and  Tangents,  Natural  Sines  and  Natural  Tangents, 
the  Traverse  'I  able,  and  a  full  and  complete  set  of  Excava- 
tion and  Embankment  Tables,  together  with  numerous 
other  valuable  tables  for  Engineers,  etc.  Eleventh  edition, 
revised,  i6mo,  full  morocco I  50 

SHELLEN  (Dr.  H.)  Dynamo-Electric  Machines.  Translated, 
with  much  new  matter  on  American  practice,  and  many  il- 
lustrations which  now  appear  for  the  first  time  in  print. 
8vo,  cloth,  New  York .". (In  press) 

SHOCK  (Chief-Eng.  W.  H.)  Steam-Boilers :  their  Design, 
Construction,  and  Management.  450  pages  text.  Illustrated 
with  150  wood-cuts  and  36  full-page  plates  (several  double). 
Quarto.  Illustrated.  Half  morocco 1500 

SHUNK  (W.  F.)  The  Field  Engineer.  A  handy  book  of  prac- 
tice in  the  Survey,  Location,  and  Track-work  of  Railroads, 
containing  a  large  collection  of  Rules  and  Tables,  original 
and  selected,  applicable  to  both  the  Standard  and  Narrow 
Gauge,  and  prepared  with  special  reference  to  the  wants  of 
the  young  Engineer.  Third  edition.  I2mo,  morocco, 
tucks 250 

SHIELDS  (J.  E.)  Notes  on  Engineering  Construction.  Em- 
bracing Discussions  of  the  Principles  involved,  and  Descrip- 
tions of  the  Material  employed  in  Tunnelling,  Bridging, 
Canal  and  Road  Building,  etc.,  etc.  I2mo,  cloth  . .  I  50 

SHREVE  (S.  H.)  A  Treatise  on  the  Strength  of  Bridges  and 
Roofs.  Comprising  the  determination  of  Algebraic  formu- 
las for  strains  in  Horizontal,  Inclined  or  Rafter,  Triangular, 
Bowstring,  Lenticular,  and  other  Trusses,  from  fixed  and 
moving  loads,  with  practical  applications  and  examples,  for 
the  use  of  Students  and  Engineers.  87  wood-cut  illustra- 
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